Using some JSON + javascript and the tibia.wikia.com API i was able to get all books from tibia, or so to say, from wikia.
Total of 1007 books/documents that are listed in wikia.
Result of that script can be found at my website:
All books from wikia by elkolorado
#edit (2023):
I've made the books into website, where you can search for keywords:
Tibia Libraries by Elkolorado | elkolorado.github.io/tibialibraries
This idea has been later expanded by s2w/cony, and he managed to obtain more books from various wikias, along with other engine to search for npc transcripts:
Tales of Tibia | LibSearch
Tales of Tibia | Npc Transcription Search
For raw data refer to s2w/tibia github
Meantime I made other website,
Tibia Nodes by Elkolorado | tibia-nodes.vercel.app
that show network graph of npc mentioning eachother, with an ability to add keywords and it connections to the graph, and ideally filtering them by location/update (as shown example 1|2) It is at development still, but you can play with it. Clicking on NPC node show his transcription.
To make the term "longest" I determined that we gonna search for the maximum characters per book.
Then, using simple sorting I was able to tell that the longest/thickest book ever in Tibia is:
The_Amazons_Vol.3_(Book)
Contaning total of 3968 characters.
Or 673 words.
You can find it in library in Carlin, below the Tibra temple, west of depot.
So to say, I made top10 list of longest books in Tibia. (Book - Characters)
Then to make it closed, the shortest book ever in Tibia is:
Goldfinger_(Book)
Contaning just the text Goldfinger making it 10 character long.