A copy of this book can also be found in the Lakeview Hotel. It's on the glass roof of the restaurant. It is hollowed out and contains the can opener for the puzzle in room 205. When looking at it after it falls down some of the text is readable. The text contains parts of the description of Gremory, as well as part of the incantation needed to summon the demon.
Thank you to Mark Rasmuson on Unsplash for the image used in the thumbnail.