I'm not an Apple person either, so I have to ask, where does Apple expect a user to store their files by default outside of the App folder structure?
Is it iCloud (which I do not use, and could not use without paying them more money as 5GB default is not enough for my ST3 backups)?
If I draw the parallel to the Windows world, apps will generally default to storing stuff in the user's "My Documents" folder on the local device, which in current veresions of Windows is usually being backed up to OneDrive. What is the equivalent on iOS?
Like Damir, on Windows and Android devices, I just create my own folders on these OS's to put stuff in a consistent, reliable, 'won't be deleted by app uninstall' location. I'll probably do same on my iPads.