[FEATURE REQUEST] Local data encryption

Is your feature request related to a problem? Please describe.
Quite often these applications are used to scan highly sensitive documents (esp Card Wallet) - existing on-device unencrypted can be a security risk

Describe the solution you'd like
Local database encryption by default for scanned-but-not-exported documents/cards
option to export PDFs with password
the easiest development-wise might be to have the user be able to set a global password, stored locally (encrypted via fingerprint/android unlock) and have this global password apply to everything exported

Describe alternatives you've considered
An application to encrypt once exported, though no alternative solution can exist for the apps' internal scans outside

Additional context
I'm a big fan of OSS card wallet and my suggestion largely stems from that, as I am keeping these files for as long as my phone lives. I'd like it to be as secure as possible

I have not checked the source to see if you using file-based encryption already for application files, so ignore that part if you are!

Thanks!! Love your work

No files, tests, or entry points are named; first map how scanned documents are stored and exported on Android, and review the eight-comment thread for an agreed scope. Done would require a maintainer-approved design covering local storage encryption, device authentication or password handling, and password-protected PDF export, with tests for each behavior.