How to copy iBooks files from my old iPhone to the new one?

PDFs in the iBooks are not included in a backup, neither iTunes nor iCloud. If you still have your old phone then connect it to your computer's iTunes and do File > Devices > Transfer Purchases (that should copy PDFs and/or epubs in the iBooks app, not just actual ibooks), and if using a Mac with iBooks on it then do File > Move Books From iTunes in it - restoring your old phone's backup should then be able to copy them onto the new phone (the restore looks to pick them up from your computer's iTunes/iBooks library), or you could just sync them to your new phone

You posted this to the old Apple notebook computer forum. I've asked this be moved to the iBooks for iOS forum.

Apple recycled the name from its 2006 and earlier notebook computers, when creating its eBook format.