I received a password protected PDF file. I opened the PDF from Gmail in a Firefox browser session. Entering the password to open the PDF file triggered the 1PW login auto-save.
I wasn't sure if this is expected behavior, but it seemed a bit odd to me. I don't think 1PW4 behaves this way, and while I guess I could see a case for wanting to save password protected files' password, it does seem like a great way to bloat a vault with junk.
1Password Version: 1Password 7
Extension Version: Not Provided
OS Version: Win8.1
Sync Type: Dropbox