When you are to hit a mob with an enchanted book with let's say, fire aspect, the enchanted book will actually burn the mob, or with knockback for example knocking it back.
MCPE-17287
Enchanted Books Have Effect of Enchant
Resolved
Duplicate
0
Thank you for your report. This issue was, however, submitted earlier as MCPE-11204. Please perform a search next time to make sure your bug hasn't already been reported. The parent issue can easily be found by searching for "mcpe unresolved enchanted book".