What are ParsedPPD files

[Norm]

Trying to diagnose if there is a printer problem or other....

During a recent Restart: in the recovered Trash there were about 50 or
more files titled "ParsedPPD (then a number)".

Background:

Apple Mail froze for no apparent reason. No viewer. No
response. Noted that Time Machine was running at the time.

Did a Force Quit.

Decided to Restart computer.

Startup stopped at beginning of reboot with a dialog saying something
about rebuilding boot caches and it would take some time. I waited for 5
minutes and when it was still hung (nothing on screen other than desktop
background and cursor), I did a Force Restart. That completed and all
seems fine.

I've never seen that dialog before. Wish I had time to record it in
full. Does that indicate any problems?

And in the recovered Trash there were about 50 or more files titled
"ParsedPPD (then a number)".

Since then, if I do a Restart I will also find these ParsedPPD files.

Thank you for any  analysis or suggestions.