You have to kill enemies and then read the book to acquire new pages.
1. 10 Jungle leapers
2. 10 Swamp feeders
3. 8 Toxic water skaters
4. 7 Underbrush fiends
5. 8 Thule sattars
6. 8 Bitter blooms
7. 6 Forest Creeps
8. 7 Thule sattars
9. 5 Evol Ew warders
Reward was a completed book to put in your house and about 3% experience at level 47.