Unable to copy pdf's from iPad to PC

I have a large number of pdf's that I have saved onto my iPad using the Acrobar Reader Mobile and whihc I can view and move into folders in Reader.  However they're not visible in the iPad's native Files app and if I try to access them in iTunes by File Sharing they also don't appear so I'm unable to copy them onto my Windows 10 PC.

Any suggestions please?

Simon