The font-capabilities in FOP is summarized by Apache in the following link:
The Adobe PostScript and PDF Specification specify a set of 14 fonts that must be available to every PostScript interpreter and PDF reader: Helvetica (normal, bold, italic, bold italic), Times (normal, bold, italic, bold italic), Courier (normal, bold, italic, bold italic), Symbol and ZapfDingbats.
The following font family names are hard-coded into FOP for the Base-14 font set:
Helvetica
Times
Courier
Symbol
ZapfDingbats
Please note that recent versions of Adobe Acrobat Reader replace "Helvetica" with "Arial" and "Times" with "Times New Roman" internally. GhostScript replaces "Helvetica" with "Nimbus Sans L" and "Times" with "Nimbus Roman No9 L". Other document viewers may do similar font substitutions. If you need to make sure that there are no such substitutions, you need to specify an explicit font and embed it in the target document.
When you select a font in Digiforms Designer, all PDF default fonts are indicated by a PDF icon. They can be used directly for PDF production without the need of embedding font information.
Note the PDF icon indicating that Helvetica is a standard PDF font
If you wish to use other fonts, the font-data needs to be embedded in the PDF document.