I'm doing this inside a Dockerized CUPS so may not work as hoped for you.

Install the non snap version of CUPS

Login via SSH or get a terminal up and copy cups-pdf.conf to cups-pdf-[slug_name_here].conf

e.g.

Open cups-pdf-test.conf and edit the out folder

Note: When you change the output folder, and try to print, you may be stopped by apparmor. You will probably need to modify the apparmor policy to allow the write to the custom directory https://askubuntu.com/questions/1263902/how-to-quickly-modify-cups-pdf-printer-output-folder-setting

Login to the CUPS website this is usually https://localhost:631/admin if you are on the Ubuntu computer I think you need to login as a member of the lpadmin group or root in my case in the docker container the URL is https://localhost:7525/admin

On the Adminstration Tab click Add Printer

You should see a local CUPS-PDF printer with (Virtual [slug_you_gave_cups_pdf_conf])

e.g. CUPS-PDF (Virtual test Printer)

Instead of choosing a Make upload a Cups PDF Printer Definition file you can find this in /etc/cups/ppd/PDF.ppd or

run driverless against the default Cups PDF Printer as follows

driverless http://localhost:631/printers/PDF > ~/PDF.ppd

Modify or just Set the Defaults

Instead of selecting Local Printers (if the copied cups-pdf-test.conf doesn't show up). You can also use AppSocket/HP JetDirect to specify the url to the printer as follows