Lost PDFs from iBooks on ipad
If the iPad was backed up to iCloud or to a Mac recently you should be able to recover from the backup.

If they were put on there from the Mac and you did not delete them from the Mac then you should be able to put them back.

If they were purchased from the App Store some how, then you should be able to reinstall them from whatever app you bought them with.


  If the only place you had them was on the iPad and it will not turn on
  or you can not connect to a Mac to back it up, then whatever was on
  that iPad is gone.