sending a fax from networked HP Officcejet Pro 8500

[Gary Aitken]

I've got an HP Officejet Pro 8500 sitting on the local network.
Web interface allows me to scan and save a document as a pdf.
Web interface also has way to set up fax forward as email or save
in a network-accessible directory.
I'm interested in sending a pdf as a fax.
There's no equivalent in the web interface for sending that I 
can find.
The proprietary software for mac and windoze apparently knows how
to send a fax.
My searches turn up nothing helpful.

anyone know how?