I added some PDFs from iTunes to my iPad and the ones already on it disappeared. When I tried to sync them back, I get the message they weren't transferred because they cannot be found. They are all showing up in the iTunes library now. Now all I have on the iPad are the ones I just added.
There can't be anything wrong with the ones I lost because they worked fine on my iPad before they were lost to it. How can I get the lost PDFs that are in iTunes to sync to my iPad Air?