Preview is automatically assigning password to saved PDF files

This thread is a year old. The PDF locking bug in Preview appears to be fixed in Sonoma. See Problems with encrypted PDF - Apple Community

This is a feature/bug in Preview. If the original PDF has any kind of security attached, then any modification to the file will set it in fully locked mode.

With respect to what you are doing, the behaviour in Preview makes sense. If someone is putting restrictions on a PDF document, that should prevent people from slicing and dicing them. Most people encounter this bug when they are trying to use a fill-in PDF. Locking the document is clearly inappropriate in that case.

You might need to wait more than one minute for a response.

The Bug in Preview LIVES ON!

Start filling out a .pdf on the web using Safari; File -> Export to PDF. Open Preview, File -> Open (select file previously exported). And I am presented with "The document is password protected. Please enter the password below."

Of course, I have no idea what the password is because someone else set it so that I could fill out the form, save the form, print the form while not being able to modify the form itself.

Apple - this is an ongoing issue. Please fix and please help users who are losing valuable time and data as a result. I have a traumatic brain injury and there is no way I will be able to recreate the contents of the form I filled out. This is unacceptable. PLEASE HELP!

So called "unlock tools" only serve to steal your data. And code to supposedly flip the encrypt switch and thus remove the requirement which Preview levied to open the file went on to delete the contents of the file.

Either remove Preview from your offerings or fix it.