To fix my computer, I think I'll have to reinstall my defective Print to PDF file. So far I haven't managed to find a way to do this - everything I read tells me how to get Print to PDF working - nothing on how to download and reinstall actual Print to PDF file.
Can't you just deselect "Print to file" in the optionalfeatures.exe? REBOOT. Check if the printer is gone. Run optionalfeatures.exe again and select "Microsoft Print to file" again?
I tried it here in both production Windows 10 Pro and Windows VM and it worked fine saving under the same pdf.
One thing you could try is to print to pdf, REBOOT, and then again try to print to the same pdf. If that works there could be some process in play (virusscanner, explorer.exe) which holds the file (although I would expect an error then).
Anyway... I NEVER advise "Microsoft Print to PDF" because it results in a much larger PDF file than all the other Print to PDF solutions. MS Print to File is notorious for creating a very inefficient PDF. So I use my own solution in combination with ghostscript (much like PdfForge, PdfCreator, Bullzip and all other free solutions).
But your problem with MS Print to PDF is still very interesting.