How to transfer files via iTunes?

I am having trouble sharing PDF or MP3 files from my Win 10 PC to my iPad (3rd gen with IOS 9.3.5) or my iPhone 6s+ using iTunes 12.8.0.150 on the PC. iTunes shows home sharing enabled for both devices. But if I go to the iTunes Music or Books directory for either device (with the devices connected), select File>Add file to library... and then select an MP3 or PDF in the add file dialogue, nothing happens and no file is transferred. Nor will iTunes allow me to drag files into it.