r3tr0 slightly off topic but which app do you use for scanning?
@r3tr0 - I use Genius Scan and it works really well. I save it to a local folder and then upload it to my Proton Drive from the files app.
Hb1hf if you don't lock Proton Drive with biometrics/pin, it should appear as a location on any files app. Then all you have to do is ask it to make files/folders available offline and you should be done. You can lock PD again when you don't need the files anymore.
@Hb1hf - This works as you described, but I cannot easily save files. For example, if I open a Proton Drive word doc from the Files app with Collabora Office, I can make edits, but I cannot save back to Proton Drive. I would have to save a separate copy in a local drive, reupload that to Proton Drive, and replace the existing file. This is a clunky workflow for me.
On a phone, if I have to make edits in a pinch, this is fine, but not on my productivity focused daily driver device.