I formated my Mac after a few years of work and forgot to do books backup because iPad was lightly used. As a result all my books stuck on the iPad and if I want to add some new from a computer it wants to erase the existing books.
With iFile, I tried to copy books, but there are only folders, not epub files.
So is there any way to get them back or somehow combine with new iTunes library? In general I don't need those books readable on mac, just to restore and the ability to add new ones to the iPad.
Best Answer
I would evaluate a program like PhoneView to retrieve the contents you like before setting up an iTunes or iCloud backup solution so you don't end up in this spot going forward. There are probably a hundred apps to load files from iOS to a computer, so you can search for one that matches your needs pretty easily. DiskAid also seems to be mentioned regularly even though my favorite is PhoneView.
Here are some relevant details to flesh out how this will work:
I have also heard many people express happiness at iExplorer for doing the same sort of recovery / transfer of files from an iOS device. Perhaps it will do a better job with your device since you remarked that several of the suggested apps didn't work for you in the comments.