There are 4 Braille Text Locations in Vampyr. You must find the Braille Documents for Mason Swanborough's side quest (investigation) "Occult Oculus".

They are also needed to open the door to the hideout east of the cemetery and to find the collectible in there.

You start the quest by talking to the citizen called Mason Swanborough. He's in a building to the North-West of the Cemetery.

It's also worth noting that you can find all Braille Texts BEFORE ever meeting Mason or triggering his quest. They are in fixed locations and spawn regardless of whether or not you have the quest. When you hand the 4 Braille Texts to Mason he can translate the code to the hideout door for you.

Behind that locked door is a collectible. There's also one monster that holds the diary. Bring the diary back to Mason to complete the quest.

Getting the door open is mandatory to find all Collectibles for trophy / achievement "Lore keeper".