Two kinds of locks on a PDF
An open password prevents anyone from opening the document without it. This tool can unlock it, but only if you enter the correct password.
Permission restrictions are settings inside the file that ask reader apps to refuse printing, copying text or editing. Such a PDF opens without a password, and this tool can produce a copy without the restrictions. The restrictions are only a request to apps, so use this only for documents you own or have the right to edit.