Hi,
- SPOILER -
are you on day 1 or 2? If you are stuck on day 1 you should take a very close at your desk in the bookstore, the letter puzzle doesn’t have to be solved to finish day 1. If you are already on day 2 you can use the razor blade on multiple hotspots of the letter and you can use the letter on another inventory item you might be missing. To get it try the quote at the front of the letter on the book database.
Best regards Christian