The final version of The Witcher 3 does not include many of the planned books. If you have already read all the available books and it is still not enough for you, you will be thrilled with what the Witcher Book Collection mod has to offer.
This modification brings back over 70 books and documents, which the developers did not manage to implement into the game. Interestingly enough, the author of the modification did not implement the books sloppily - he placed them around the in-game world in a sensible manner. Most of the books are located in proper locations or available at particular vendors. There are also those books, which a player receives as a reward for completing certain quests.
Moreover, the modification also implements the books known from the previous installments in The Witcher series - these can be purchased from the vendor located in the city square of Novigrad. All the texts are available only in English.
The developer of this mod has added one more novelty - short descriptions of hundreds of items, in particular objects related to quests as well as books, and alchemy ingredients.
This modification can be installed either with Nexus Mod Manager or manually - by pasting the contents of the downloaded archive into the Mods folder.