This guide is considered complete, only the collectable exact location are not listed but you are welcome to make a comment so I'll add them on each of the chapters.

You will most likely need at least 2 playthroughs to get all achievement except one which will require to finish a challenge map with an epic score.

Enjoy the game in whatever difficulty you want, and focus on getting everything you can.
You can also try to get achievement prior to playthrough 2 but in your second playthrough you will only do the main objectives and therefore it will be easier.

Focus on the following :
Obsessive Compulsive
Stole all loot and collectibles in a single chapter.
Sleight of Hand
Picked 100 pockets in a single playthrough
Working Overtime
Completed all client jobs in The City
Dastardly Deeds
Completed all Basso Jobs in The City
Finders Keepers
Discovered all secret areas
Cache Dispenser
Used 40,000 gold
Predatory Drive
Finished the game in 15 hours or more

You will want to stack all these achievements and focus on main objectives only.
You will need to create custom settings of 700 points or higher.
It is best to stack the following one as they are required for both related achivements :
No focus (50 pts)
No kills or Knockouts (170 pts)

Base Difficulty - Master
No focus (50 pts, so you won't require to unbind that key)
Stealth takedowns only (50 pts, since you will try to stack the no kills and no knockout)
Specialty arrows only (50 pts, blunt/water/fire/rope arrow only + flash bomb)
No food or poppies (100 pts, you won't be able to use them only sells them, also your health should replenish between chapters)
Expensive Resources (70 pts, the only thing I bought was all the tools for 2000g)
No upgrades (100 pts, you can still buy your tools)
No kills or knockouts (170 pts, straitghforward)
No alert/b] (170 pts, dogs and birds also count)

The customs settings are explained in the section called Difficulty level selection in the gamepressure guide of Thief.

/!\ If you are not opting for customs settings, you can opt to unbind the key for the focus ability /!\

Focus on the following :
Hard Times
Finished the game on Master difficulty
Something to Prove
Finished the game with a custom difficulty of 700 points or more
Clear Headed
Reached the final chapter without using the focus ability
A Moral Victory
Finished the game without a single kill or knockout
Mint Condition
Finished 3 consecutive chapters without taking damage
Child of the Shadows
Finished a single chapter without alerting anyone

Modesty denied1
Scored an epic 5,000,000 or more in a Challenge Map.

The easiest way to get it is to choose the following challenge :

You just need to take out all of the guard and get some loot.

The related guide and its video can be found on trueachievements regarding the modesty denied achievement.

If you want to restart the chapter you are currently in, you just need to either use the auto-save of the chapter start or choose 'Exit to the city' and then interact again with the Chapter area.
If you want to replay a chapter, you just need to re enter the area that triggered that chapter.
For that I suggest you use one of the following guides :
https://steamproxy.net/sharedfiles/filedetails/?id=233717834
https://steamproxy.net/sharedfiles/filedetails/?id=272186385

If you want to restart the client job you are currently in, you just need to choose 'Exit to the city' and then interact again with the client job area or maybe you can also use the auto-save to restart at the start of the job.
If you want to replay a client job, you just need to re enter the area that triggered that client job.
For that you might need advance a chapter if you already completed the client job but missed some stuff. Check the two guides above on where to find the area again.

There are only 206 documents to be found on the 215 listed in the game, also they are not required for any achievement.

Here are the one that are high likely missable :

Just ensure that you get this entry after finishing the prologue at the start of the game. You found it where you jump from the rooftop to a window in a house, the note is on the table. When you leave the house you hear a woman complaining to a man peeing.

The list come from the following guide and since it is not easy to read I've noted them all below.
The guide is from the forum of psnprofiles that list all the newspapers.

If you want to get all 206 documents, I suggest that you focus on those newspapers as most of them are missable very early.


06. The Benefits of Strict Curfew
Found at the start of the chapter on a brown briefcase in a corner.
Note: You can also get it after Chapter 1: Lockdown

04. Clock Tower Stops Again!
Found during the jewelry location, you need to follow the underpass which is on the alley opposite of the jewelry store. Follow the alley until you find this newspaper next to a pile of bags before using the vent.
Note: You can also get it after Chapter 1: Lockdown

05. Who Watches the Watch Hounds?
In the jewelry store, at the top floor in the room opposite the bird cage, the newspaper in on the bed.
Note: You can also get it after Chapter 1: Lockdown

03. Lockdown!
After you drop down from the jewelry store, the newspaper is on the bench. Take it before exiting the chapter through the window.
Note: You can also get it after Chapter 1: Lockdown


19. Star Of Auldale Necklace - Under Bank Protection
Inside Clock Tower when you appears after finishing the first chaper. Found on the lower level on a dusty table. Note: This is part of the DLC. You might need to download it first for the newspaper to appears in the game.

01. Treason!
Location: Stonemarket/Basso's Office
On the desk at the opposite of Basso, wich is found in the Crippled Burrick area.

02. Northcrest Unbowed!
Location: Stonemarket/The Crippled Burrick
Found in the tavern, on the bar.

07. No Old Gods for the New City!
Location: Stonemarket/The Chapel
On the desk next to the Beggar's Queen.

03. Lockdown!
Location: Stonemarket/Watch Council Office
Details: Enter this through the window facing the Clock Tower directly. On the desk downstairs. Note: You can also get it in Chapter 1: Lockdown

04. Clock Tower Stops Again!
Location: Stonemarket/Blackfurrow
Details: On a desk in the attic you enter through a window on the rooftops. The window is next to a chimney. You will hear a conversation between sisters about their mother's ring.
Note: You can also get it in Chapter 1: Lockdown

05. Who Watches the Watch Hounds?
Location: Stonemarket/Sick Willy’s Townhouse
Details: On a desk at the far end of the house. This place is one of the Basso's Jobs - Sick Willy.
Note: You can also get it in Chapter 1: Lockdown

06. The Benefits of Strict Curfew
Location: Stonemarket/Troy's Apothecary
Details: On the desk in the room where the two guards are. This place is one of the Basso's Jobs - Medical Misery.
Note: You can also get it in Chapter 1: Lockdown


You will need to get the disappearing poet job from Basso to get the last newspaper priori to Chapter 2.

08. Break-In!
Location: Stonemarket/Baron’s Way South
In the room where there are a lot of stuffed animals. Reached with a rope arrow, and interacting with a window, not far from the merchant icon on the map.

12. Carnival Boat High and Dry!
Location: South Quarter/Fish-Hawker’s Market
Details: In the hidden bar which you enter by pressing a button in a safe that is revealed by pressing another button. Inside it's on a barrel.

11. Literary Greatness Lost
Location: South Quarter/Old Postmaster’s House
Details: This place is located in Fish-Hawker's Market, reached with a rope arrow. Press a button to reveal an opening on the ceiling. Upstairs it's on the end table next to the bed.

10. The New Watch Laws and You!
Location: South Quarter/Skinmarket
In a room near where a single woman is standing close to a fire. This place will be one of the Basso's Jobs - Fit for a Queen, later in the game. It's the window opposite the one that let you go to the riverside baron way north.

09. Beware of Over-Active Imaginations
Location: Riverside(South Quarter)/Poet’s Abode
You will need Basso's Jobs - The Disappearing Poet in order to enter this area.
On a desk downstairs. This place is one of the Basso's Jobs - The Disappearing Poet

13. Turn Not to Protest!
Location: Riverside(South Quarter)/Baron’s Way South
Details: In a cabinet in an apartment which you reach with a rope arrow. You need to enter this apartment through one window and exit through another to get to one of the Vitori's Client Job.

14. Charlatan Remidies!
Location: Riverside(South Quarter)/Siren’s Rest
Details: Upstairs next to Vitori on a table.

15. Blackhands Of Riverside!
Location: South Quarter/Eelbiters Squat
Details: On the table in the room with a safe. This place will be one of the Basso's Jobs - Poor Protection. BUT by the time you won't be able to get the newspaper.


17. Riots In Dayport!
Location: South Quarter/Canal
On an outdoor counter to your right right after you climb up to Canal from Fish-Hawker's Market.

18. Manhunt!
Location: South Quarter/Raker's Ditch
Details: Across from the start point for Chapter 3, in a room that has a 4-tumbler lock, on a barrel.

16. Fires of Revolution!
Location: Riverside(South Quarter)/Siren’s Rest
Note: Ground floor, behind the bartender.

Secret 1/73
Can't be missed
After you get into the apartment, you need to examine the painting on the wall, press two switches and take the ladder to the attic.
Secret 2/73
Document - Stonemarket - Manuscript
Common loot
After you get to the bookbinders' you need to locate the interactive row of books (behind the counter) and press the button.
Secret 3/73
Can't be missed
After you make it into the fence's apartment, you need to find the interactive row of books, pull the correct one and walk into the unlocked area.
Secret 4/73
Collectible - Flowers Eternal
You need to reach the second location in Jeb's hideout, press the button behind the vase and examine the stash, where there is the iris brooch (Flowers Eternal).
Secret 5/73
Document - Hangman's Memoirs
Common loot
After you walk into the apartment, you need to locate the interactive row of books, pull one of them and walk into the newly-unlocked secret area.
Secret 6/73
Collectible - The Court of Montonessi - The Insatiable Appetite
Poppy
You need to access the building's basement, locate the venting shaft at the crates and press the button, which will unlock a secret area.
Secret 7/73
Can't be missed
You only need to access the Watch Station (it is a good idea to find the box disable all of the trap beforehand).
Secret 8/73
Collectible - Mortal Coil
Common loot
You need to access the crypt in the cellar (use the shaft, hit the arrows against the interactive buttons and climb down the rope to the very bottom).
Secret 9/73
Can't be missed
Document - Wax Witch's Journal
Document - Candle Wax Ritual Book
Common loot
Poppy
You need to take the venting shaft to reach the witch's hideout.

https://steamproxy.net/sharedfiles/filedetails/?id=272186385
https://steamproxy.net/sharedfiles/filedetails/?id=233717834

Secret 10/73
Unlike most the secret, that one triggers when leaving the area.
Common loot
You need to get onto the wooden balcony surrounding one of the buildings. Force the window open and walk into the empty apartment. Approach the painting over the bed and, press the secret button, loot the side stash and exit the apartment.
Secret 11/73
Common loot
You need to start by walking over the wooden planks above one of the main streets (keep going east). This way, you will get to a shaft entrance. After you walk through the shaft, you will get into a small room.
Secret 12/73
Document - ??? - ???
Common loot
You need to make it over to the balconies above, located to the South-West of the Fish Market (there is the Watch Station and the South Quarter Postmaster nearby). Find the vertical bridge and hit the button behind it, thanks to which the wooden structure lowers. You can now explore the newly, unlocked secret area.
Secret 13/73
Document - Newspaper - Literary Greatness Lost!
Collectible - The Mortal Coils - Wellpool Viper Bracelet
You need to use a rope arrow to access the South Quarter Postmaster building, press the secret button and get to the highest floor in the building.
Secret 14/73
Collectible - Pinned Castinets
Focus point
Common loot
You need to explore the area to the East of the fish market, press several buttons and access the derelict bar, where there is the Oil Box (Pinned Castinets), among others.
Secret 15/73
Common loot
You need to locate a venting shaft entrance, in the North-Eastern part of the fish market (close to the dog cages) and take it to reach a secret room.
Secret 16/73
Common loot
Near the main street, you need to find an entrance to a small venting shaft, which will take you to a small room.
Secret 17/73
Common loot
It ssems to trigger only once?
You need to explore the Southern part of the main street (near the water) and locate the grate of the venting shaft. Walk through the shaft to reach a storage area.

https://steamproxy.net/sharedfiles/filedetails/?id=233282339
Remain undetected
Extinguish 9 flames
Headshot 4 threats
Lift all 60 loot items.

There are 4 collectables to be found, please check the above guide which won't spoil the exact location. Otherwise you can use the guide of Thief on gamepressure that will spoil everything.

https://steamproxy.net/sharedfiles/filedetails/?id=233282339
https://steamproxy.net/sharedfiles/filedetails/?id=239224142
https://www.youtube.com/watch?v=RnrNDN1EAOA

Remain undetected
Pick 10 pockets
10 combat takedowns
Lift all 71 loot items

There are 5 collectables to be found, please check the above guide which won't spoil the exact location. Otherwise you can use the guide of Thief on gamepressure that will spoil everything.

Secret 18/73
On your way to the foundry building, you need to stop in the Dust Yard location and explore the cottage to the left.
Secret 19/73
Right after you walk through the shaft and make it onto the foundry's Office Level, climb up the stairs and explore the room at the end of the corridor.
Secret 20/73
During your exploration of the second part of the foundry (Manufacturing Area), you need to reach the platform above using a rope arrow, where there is the Daisy Brooch (Flowers Eternal).
Secret 21/73
During the exploration of the second part of the foundry (Manufacturing Area) you need to reach a secret room in the North-Eastern corner of the building and break into the safe, in order to obtain the Automaton's Soul (Unique Loot).
Secret 22/73
During the exploration of the second part of the foundry (Manufacturing Area) you need to explore the North-most corridor and climb over the metal objects to reach a small area under the ceiling.
Secret 23/73
During the exploration of the second part of the foundry (Manufacturing Area) you need to explore the central part, i.e. the one where there is the scientist, among others. Find an interactive catch, use the rope arrow and make over the rope to the plank under the building's ceiling.
Secret 24/73
During the exploration of the third part of the foundry (Furnace Hall) you need to explore the side room and collect the Diamond Circle (Serendi Stone Circles).

https://steamproxy.net/sharedfiles/filedetails/?id=233282339
https://steamproxy.net/sharedfiles/filedetails/?id=1285580345

Remain undetected
No kills or knockouts
5 Aerial Takedowns
Lift all loot items

/!\ I've only listed 2 collectables below, so please refer to the following guides. /!\
There are 5 collectables to be found, please check the above guide which won't spoil the exact location. Otherwise you can use the guide of Thief on gamepressure that will spoil everything.

Secret 25/73
After the beginning of the chapter, you need to follow the main corridor, find a venting shaft along your way, and enter.
Secret 26/73
After the beginning of the chapter, you need to use the wirecutter on the box and unlock access a side room. Additionnaly you can access it with Secret 27 with the first gap you encounter while climbing.
Secret 27/73
While exploring the first part of the undergrounds (the beginning of the chapter), you need to locate a big vertical shaft, use a rope arrow and climb up the rope to the very top. Then, jump towards a small ledge.
Before entering the House of Blossoms with either route, be sure to collect the loot before proceeding. (If you wish to get all the loot.)
Secret 28/73
Collectible - Unique loot - Ancien figurine
While exploring the Underground Ruins, you need to reach the corridor that leads up to the place where the Ancient Figurine is hidden (Unique Loot).
Secret 29/73
Collectible - Memories of the dead - Stonemason's Memory
After you reach the scriptorium in the Underground Ruins, locate the interactive row of books and unlock access to a secret side chamber (among others, there is the Stonemason's Memory there).

https://steamproxy.net/sharedfiles/filedetails/?id=233282339
https://steamproxy.net/sharedfiles/filedetails/?id=1285608066&searchtext=chapter+2

Remain undetected
Pick 8 pockets
10 Kills of knockouts
Lift all loot items

/!\ I've only listed 1 collectable below, so please refer to the following guides. /!\
There are 6 collectables to be found, please check the above guide which won't spoil the exact location. Otherwise you can use the guide of Thief on gamepressure that will spoil everything.

Secret 30/73
Collectible - Serendi Stone Circles - Lapis Lazuli Circle
Along your way to the Architect's house, you need to reach the lower floor, where there is, among others, the lapis lazuli circle (Serendi Stone Circles).

Secret 31/73
After you get to the gardens in front of the Architect's estate, you need to enter the cottage on the left and unlock the sewers access.

Secret 32/73
Along your path to the Keep, you need to reach the Pipeline. Start moving over the balcony, slowly, to prevent it from collapsing, to reach the secret area after several moments.

Secret 33/73
After you reach the location with the Grand Safe (still before you lower it) you need to explore the balcony at the back of the hall.

https://steamproxy.net/sharedfiles/filedetails/?id=233282339
https://steamproxy.net/sharedfiles/filedetails/?id=239894247

/!\ I've only listed 3 collectable below, so please refer to the following guides. /!\
There are 6 collectables to be found, please check the above guide which won't spoil the exact location. Otherwise you can use the guide of Thief on gamepressure that will spoil everything.

Secret 34/73
Collectible - Flowers Eternal - Rose Brooch
Right after you reach the first part of the Women's ward, you need to make your way to the very bottom of the shaft on the left, i.e. to the location where there is, among others, the Rose Brooch (Flowers Eternal).

Secret 35/73
Collectible - The Court of Montonessi - The Repulsion of Civility
After you reach the Men's ward, you need to take all the steps necessary to collect The Repulsion of Civility painting (The Court of Montonessi).
Secret 36/73
You need to examine the "magical" cabinet in a bit bigger room, in the North-Eastern corner of the Men's Ward (open it, close, wait until you hear a man's voice and open again).

Secret 37/73
While at the Treatment Center (right after you have explored room 3F) you need to reach the hall with the imprisoned scientist and collect the magnifying glass from the top of the cage.

Document
Escape Note Cell Release Room (Desk)
Elevator Lock Cell Release Room (Desk Drawer)
Extracting The Primal Cell Release Room (Cabinet Doors) **
Sensory Deprivation Corridor (Wall)
Transfer Request Room 3F (Drawer)
Calibration Room 3F (Wall)
Knocking in Pipes Room 3E (Drawer)
Sterilisation Room 3E (Safe Spot)
Lobotomy Room Room 3D (Trolley)
Shock Therapy Room 3B (Wall)
Treasure Vent (Floor)

** The note is found in Baron Northcrest instead of Chapter 5

Secret 38/73
Collectible - Unique loot- Mechanical Eye
While exploring the old prison, you need to reach the rooftop of the central bridge, where there is, among others, The Mechanical Eye (Unique Loot).

https://steamproxy.net/sharedfiles/filedetails/?id=233282339
https://steamproxy.net/sharedfiles/filedetails/?id=415535186

There are 6 collectables to be found, please check the above guide which won't spoil the exact location. Otherwise you can use the guide of Thief on gamepressure that will spoil everything.

Secret 39/73
While exploring the gardens at the beginning of the chapter, you need to unlock access to the Drainage and follow it.
Secret 40/73
You need to reach the secret chapel (Old Family Chapel) on the first floor of Northcrest's estate (it requires you to examine one of the paintings in the Western corridor).
Secret 41/73
Along your way to the ceremonial hall, you need to explore the corridor in the Northern part of the first floor and make your way to the shaft located under the ceiling. Follow that shaft to get to a seemingly inaccessible room.
Secret 42/73
After you reach the demolished ceremonial hall, you need to locate the scaffolding that will allow you to reach an urn as a loot.
Secret 43/73
After you get to the lab, you need to use the rope arrow to reach a separate ledge, where there is, among others, the Braggart's Memory (Memories of the Dead).

https://steamproxy.net/sharedfiles/filedetails/?id=233282339

There are 4 collectables to be found, please check the above guide which won't spoil the exact location. Otherwise you can use the guide of Thief on gamepressure that will spoil everything.

Secret 44/73
You need to explore the Northern side of the cathedral's main hall and after you disable the traps (the box), use the ropes to reach a small room with a chest.

Secret 45/73
After you reach the first part of the Hidden City (Loading Docks Exterior), you need to use the drawbridge to get to the place where the City Artifact is (Unique Loot).

Secret 46/73
While exploring the highest part of the Hidden City (Loading Docks Exterior), you need to jump across a platform, inside there is a rope arrow spot to get the loots.

Secret 47/73
While exploring the main area of the catacombs (the one with the monsters), you need to reach the lower ledge with the locked door. Enter the room, where there is the Bronzehead Bracelet (Mortal Coils).

https://steamproxy.net/sharedfiles/filedetails/?id=233282339

There are 2 collectables to be found, please check the above guide which won't spoil the exact location. Otherwise you can use the guide of Thief on gamepressure that will spoil everything.

Secret 48/73
While exploring the Mine Tunnels you need to take the upper path, stop after you find an interactive rope arrow spot, extend the rope and use it to reach a seemingly inaccessible area.
Secret 49/73
After you reach the first part of the ship Treadwheel Deck, you need to climb down the stairs and locate the entrance to the optional venting shaft. Of course, you are supposed to explore the shaft.

https://steamproxy.net/sharedfiles/filedetails/?id=233717834
https://steamproxy.net/sharedfiles/filedetails/?id=272186385
Secret 50/73
Document - Bait and switches 2
Common loot
You need to find a grate of the venting shaft, walk through the shaft and reach a small room with a trapped chest.
Secret 51/73
Document - South Quarter - Smuggler's Map: Eel's End
You need to find a grate of the venting shaft, walk through the shaft and find an area with small stairs. Press the button under the stairs and approach the newly-unlocked chest.
Secret 52/73
Common loot
Food
You need to locate an interactive catch, high above, extend the rope and use it to reach the window at the building's top level.
Secret 53/73
Document - Stonemarket - Smuggler's Map: Muddler's Row
You need to examine the area around the obelisk, climb onto one of the nearby rooftops and find the place where you jump down onto the beams below. This way, you will reach an open window. Enter the apartment and shoot an arrow at the button hidden behind the bed
Secret 54/73
Collectible - The Court of Montonessi - Arrogance of Nobility painting
You need to gain access to the building, where there is the Arrogance of Nobility painting (The Court of Montonessi).
Secret 55/73
Document - Stonemarket - Smuggler's Map: Blackfurrow
You need to use a rope arrow to reach a small balcony with locked door. Open the door, enter the apartment and take a look around for a button under the desk.
Secret 56/73
Common loot
You need to explore the area around the obelisk, climb onto one of the nearby rooftops and jump down a small hole, next to the ladder.
Secret 57/73
Vendor - South East
You need to explore the area at the back of the watchtower. There is a venting shaft here, which will take you to the staying place of one of the local merchants.
Secret 58/73
Common loot
The area is next to Chapter 1. You need to explore the area near the passage (crates) between the Baron's Way and the central part of the City. There is a venting shaft here. Walk through that shaft and use a rope arrow to reach the room above.
Secret 59/73
You need to explore the area around the crates that allow you to travel between the Baron's Way and the central part of the City (around Ector's Emporium). Locate the venting shaft and walk through.
Secret 60/73
The secret trigger only when you got this unique loot.
You need to take all the steps necessary to gain access to the Golden Keep (Unique Loot).
They are explained in the wiki called thiefgame fandom regarding the Golden Keep.

https://steamproxy.net/sharedfiles/filedetails/?id=233717834
https://steamproxy.net/sharedfiles/filedetails/?id=272186385
Secret 61/73
Common loot
You need to walk over the balconies above to get to the apartment at the upper floor, located to the east of the watchtower. Locate the interactive row of books, pull the right one and enter the newly-opened room. Finally, use a rope arrow onto the catch above and reach the upper level.
Secret 62/73
Common loot
You need to start at the gate between the Old Quarters and the Clock Tower Plaza (crates). Look up, use the sharp arrow after the bridge lowers and two rope arrows on the interactive catches. Start climbing now and reach one of the windows above.
Secret 63/73
Collectible - Pinned Castillets
Document - Graven Notes
Common loot
You need to explore the area to the South-West of the watchtower, close to the gate, thanks to which you start the seventh, and the eighth chapter. Make it over to the balconies above and jump towards the window into the apartment, where you can find, among others, the Dawn Gauzy (Pinned Castinets).
Secret 64/73
Common loot
You need to take the alley located to the North of the watchtower. Keep looking around, as you go, for a hole in ceiling and use a rope arrow to reach a small room.
Secret 65/73
Common loot
You need to locate two catches arranged side-by-side, and extend two ropes (rope arrows). Make your way to the very top and use both ropes to reach the window into the closed drugstore.
Secret 66/73
You need to make your way to the rooftops in the Northern part of the Old Quarters. Find the bridge that you can lower, shoot the sharp arrow at the button and enter the apartment. Locate the interactive row of books here, pull the right one and explore the closet with the corpse.
Secret 67/73
You need to make your way to the rooftops of the Northern part of the Old Quarters. Find the hanging rope and climb up, to the very top.
Secret 68/73
Collectible - Pinned Castinets - Ghost-Girl
Common loot
You need to make your way to the rooftops of the Northern side of the Old Quarters. Find the venting shaft and walk through it. After you walk into the apartment, press the button. Now, extend the rope, climb down to the very bottom and jump towards another window. You will walk into the apartment, where there is, among others, the Ghost-girl (Pinned Castinets).

https://steamproxy.net/sharedfiles/filedetails/?id=233717834
https://steamproxy.net/sharedfiles/filedetails/?id=272186385
Secret 69/73
Common loot
You need to walk through the window and walk into the warehouse that you visit during the "A Grave Matter" mission, thanks to which you will end up above the main street. Jump towards the balcony to the West and enter through the window of the neighboring building.
Secret 70/73
Common loot
You need to go to the building located to the left of the gate that you take to start chapter six. Find the interactive window and enter the building.
Secret 71/73
Document - Stonemarket - Bait and switches 4
You need to explore the area to the left of the blazing Watch Station (the one with the obelisk in front of). Climb down the rope and take the venting shaft. Find the place where there is an opponent with a document (you do not need to steal it to "complete" the secret area).
Secret 72/73
Vendor - Market Street
You need to explore the area to the left of the blazing Watch Station (the one with the obelisk in front of). Climb down the rope and take the venting shaft. Find the place where there is one of the merchants.
Secret73/73
You need to explore the South-Eastern side of the district, i.e. the area at the back of the warehouse that you visit, during the "Grave Matter" side mission. Climb up the crates and reach the corner where there is a poppy.

There are only 206 documents to be found on the 215 listed in the game, also they are not required for any achievement.
The bank heist - 13 documents
Baron northcrest- 13 documents
Ector client jobs- 22 documents
Stonemarket- 33 documents
South quarter- 15 documents
Prologue- 1 document
Chapter 1- 2 documents
Chapter 2- 9 documents
Chapter 3- 4 documents
Chapter 4- 6 documents
Chapter 5- 42 documents
Chapter 6- 12 documents
Chapter 7- 4 documents
Newspapers- 19 documents
Vittori client jobs- 3 documents
Chapter recaps- 8 documents

For the missable documents, please check the section at the start of the guide called

For the following city documents :
Stonemarket- 33 documents
South quarter- 15 documents
You can use the following guide :
https://steamproxy.net/sharedfiles/filedetails/?id=233717834

Most of the other documents can be found using the Thief guide on gamepressure, they are highlighted in orange like the collectables. This will spoil the game.

You need to have the DLC purchased and installed.
Remain undetected
Take no damage
2 Aerial Takedowns
Lift all loot items

From Ector who is located at his Workshop in Stonemarket (Ector's Emorium)
Collectible - City Heritage Plaques - South Quarter Sluices
Remain undetected
Pick 5 pockets
1 Kills or knockouts
Lift all loot items

From Vittori who is located at the Sirens Rest in Southquarter - Riverside
Remain undetected
Take no damage
2 Combat Takedowns
Lift all loot items

From Ector who is located at his Workshop in Stonemarket (Ector's Emorium)
Remain Undetected
3 Head shot kills
1 environmental exploit*
Steal All Loot
* Shoot the box down no need to kill anyone.
Just sleep the dog and take care of the guard first.

From Vittori who is located at the Sirens Rest in Southquarter - Riverside
Remain Undetected
No Kills or Knockouts
1 Aerial Takedown
Lift All Loot Items

From Vittori who is located at the Sirens Rest in Southquarter - Riverside
Remain Undetected
Distract 4 threats
4 Combat Takedowns
Lift All Loot Items

From Ector who is located at his Workshop in Stonemarket (Ector's Emorium)
Steal all loot