The Font property displays the contents of the Fonts value list, you can see this value list in M-Files Admin > Metadata Structure (Flat View) > Value Lists. I'm not 100% sure how these values are mapped to the actual fonts installed on the server, but my guess is that the name has to match. In other words, you could try adding other fonts on the server to that value list (e.g. "Times New Roman").
I have also found this confusing, every reference that I have found towards the PDF Processor Module only discusses the one Arial font. Feedback on this would be great.