Most secure document viewer for Android?

What are the most secure document (.pdf, .txt, etc.) viewers for Android? I plan to de-Google, but I'm stuck with android for now. Does a secure app really matter if it's on a Google device anyway? I'd prefer something encrypted/password protected, and isolated enough to protect as best is possible from intrusion and exfiltration.


Threat model: domestic government, hackers/bad cyber actors, and receiving sensitive files from a party that has the potential to be compromised (socially or digitally).

I'm not …

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