Q I seem to have got my book library stuck in iTunes. Having upgraded my iPhone, I can now no longer add any more of my own PDFs to the library. Is this a bug in iTunes?
A Recent releases of iTunes have decentralised control over some of its libraries, including that for books. Whilst you used to be able to add your own PDFs and other iOS-accessible books to the Book library from within iTunes, you now need to use the separate iBooks application to maintain that library.
If you have not installed it already, obtain it as a free purchase from the App Store. Open iBooks and click on the All Books button at the top to show all items in your library, including PDF files. Take the opportunity to prune any old items which are no longer required, then add your new PDFs using the Add to Library… command in the File menu. When complete, quit iBooks and you should now be able to install those PDFs on iOS devices that are synced using iTunes.
If this still does not work, you could try creating a new collection and adding your books to that.
Updated from the original, which was first published in MacUser volume 31 issue 1, 2015.