Take my words back! PDFprotect crashed when trying to deprotect a PDF requiring a password to open. But looks like PDF key can do it (crack the password), and also can remove all kinds of PDF protection. For $39 it seems no PDF could be left protected...

Alex
3.1 GHz 13" MacBook Pro 2015, 8 GB RAM, OS 10.11.2, Office 2011, TimeWarner Cable
2.8 GHz Xeon Mac Pro 2010, 16 GB RAM, OS 10.11.2, Office 2011, LAN