If you’re prompted for a password while trying to open or print a PDF, first, make sure any ZIP files that it’s contained in are completely extracted.
This issue also happens when PDFs are opened in programs other than Adobe Acrobat or Adobe Reader. To resolve the problem, you can open the PDF with the latest Adobe Reader instead, which can be downloaded for free here:
It's important to note that you should open Adobe Reader first and then select the resource you wish to view from within Adobe Reader. To do this, open Adobe Reader and click File--> Open to select the resource from your computer. Just clicking on the PDF alone may still open the PDF in a default program.