I don't create password documents, so this is only a GUESS as to what I would do
Open your document with your password
Do a "save as" to a new document with NO password
Edit that new document
Seems reasonable but I tried that and the created file required the same password. I finally figured it out. You need go to file menu and select "save a copy". It will ask for your password then you go to the file menu and select properties and select no security. That worked.
Thanks for your input.