Do you mean file permissions, or encrypted file contents?
If you're talking about the contents, then you will have to either ask an app or module that knows how to read that particular file format, or consider the specs for each file format (if there are any).
A password in a .zip file will be completely different from a password in a word document, for example.

In reply to Re: Determine if a file is password protected by SuicideJunkie
in thread Determine if a file is password protected by slloyd

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