Sometimes vendors or clients may give us PDF documents that have been password protected and thereby preventing us from doing any markup on the document. If the password can not be removed using regular means or the password is not know a last ditch effort might be to print the PDF to a new PDF document.
Open the PDF file in a PDF viewer and then print it. Select the destination to be the PDF Printer software on your machine. (Scan Soft PDF for example) and if the document allows printing you will have a fresh new PDF with no password.