A possible workaround to a locked PDF is to invoke the Print dialog box (File>Print) but save it as a PDF instead of printing. The new PDF may be unlocked. I don't have a locked PDF to try this with, but it might work.

Jon

macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365