For the rest of us who aren’t going to be using Mavericks, here’s how to export iBooks from iPhone or iPad to your computer:
1). Get a file explorer. Usually, iExplorer should do just fine.
2). Connect your iPhone or iPad to the computer and fire up iExplorer
3). Open your iPhone/iPad as a mounted device and navigate to:
Media → Books → Purchases
The funniest thing is that you won’t be able to decipher what file corresponds to what book from your library because, like music, the file names are encrypted. Nevertheless, you can copy stuff now.
This folder method gives you access to all files including .epub, .pdf and all types you have purchased. You might want to check out epub to pdf converters to make a readable copy of the epub iBooks you’ve got.
Transfer Purchases:
There was some suggestion about transferring your iPhone/iPad purchases via iTunes so you get the iBooks on your computer. The problem is, you still can’t open them on your PC like you’d open a normal pdf file. That’s why no normal method works to export pdf from iBooks to PC.
The software mentioned above has both Mac and Windows versions. Go right here to download iExplorer.