I was using PDF Architect 4.1 to convert some files to PDF/A. Maybe I closed the program with a file still open, because Win 10 File Explorer won’t let me rename that file. It tells me that the file is still open in PDF Architect.
This may be a bug.
I restarted PDF Architect. There was no open file. I closed PDF Architect, and I still couldn’t rename the file.
I restarted my laptop, and then I could rename the file.