PDF pseudo-printing (Debian CUPS)

[Monty J. Harder]

I must be really dense.  When I look at the Control Center - Printers
in KDE, I see printers listed that include printing PDF to file, but
when I try to print something out of, say, Firefox, they don't show up
in the list of printers.  When I connect to localhost:631 and try to
add a printer, I don't see any option to add a printer as
print-to-file.  What am I missing?