I’ve had the need to append pages to PDFs encoded with DRM. A great tool for removing DRM one file at a time is a service called pdfclean for OS X, an installer of the command line utility included with mupdf’s MuTool clean. I successfully installed and used the service under Mountain Lion and found it effective. Thanks, be3n!

For macOS Sonoma and later, be3n’s tool works as an Automator app, just drop an encrypted .pdf on it. I’m having some trouble with it removed the encryption under Sonoma and am checking with be3n on a potential solution. Right now, when pdfclean attempts to remove encryption on a .pdf, it makes a new file that takes the form “old_file_name.pdf.broken” – removing “.broken” allows the file to open, but the encryption is still there.