The Secret door achievement is the only missable achievement in the game, if you finished pack 12 already and you don't have this achievement you will need to replay the whole game to get to this point.

OR you can simply download the save file I backed up just before doing pack 12 :)

If you want to download and use my save file follow these steps:

1) Download the two SaveData0 files I'm hosting on googledrive here : https://drive.google.com/drive/folders/1Bf_IPTE3X3tEA2D1B7dTVAkbOCMilwn1?usp=sharing

2) Then open up your games directory through following these steps:
2.1) Right clicking on "Dude, Stop"
2.2) Hover over Manage, and then click on "Browse local files"

3) Open the "Saves" folder

4) Move the two SaveData0 files over into this folder (if you have a secondary save file it will ask if you want to overwrite the save file, which will be required for you to use this)

Once you have loaded the save file simply go to pack 12 and start the test

1) Pull only 1 sheet off the calendar and then place the Christmas tree down

2) Make the burger WITH the pickles in the order that the guy wants it in
Bun, Meat, Cheese, Pickles, Tomato, Lettuce, and bun again

3) Pull the blue balloon out from under the tree and let it float away

4) Park the car over the white lines

5) Let the duck scenario play out, click close on the console after the emails are loaded, and then wait until the narrator starts a countdown, you must then close the game.
(If you are running on Windows you need to press Alt + F4 on your keyboard, if you are playing on a Mac you need to press Command + Q on your keyboard)

6) Simply open the game again and you will get the achievement after the narrator has a few lines of dialogue with you