Three types of books to be found in the world, recreational books, educational, and special books.
Recreational books can casually be completely read during a rest or two. A few recreational books can be flipped through and read near immediately. These types of books may only appear in the holder's inventory.
Educational books may contain world lore, creature information, increases in proficiency to the reader, or other informational benefits. This information will only appear to the reader, so make sure to share the info with the party if desired.
Special books have their own rules or directions on reading expressed in the book itself. Depending on the book, the information may be available to the entire party as well.