I humbly request that you do away with "you can't sign this document because it's already been signed"
So i click on "remove restrictions on this document" and then it asks for a password. Me no HAVE a password, WHAT password? wtf are you talking about? WHERE do i find this golden password that i've never created? wtf am I paying for this for
Sorry for the delay in response.
Author of the file may have password protected the file so no other person should be able to make changes to the document, but should have allowed to fill and sign the document. In this situation, you have to reach out to the author of the document.
To verify whether the document is restricted or not, you may open this document in Acrobat or Reader, click File>Properties, check the Security tab of properties window and check document restriction summary.