You can see the list of fonts available in your system in System Settings > Fonts
To upload new fonts, you need to a) have a suitable license to use the font and b) make sure its properties allow it to be ’embeddable’. You can upload any windows font, or TTF, OTF, or Postscript Fonts. The postscript fonts will require 2 files to be uploaded, usually a PFM and an AFM.
Please note any system fonts you find in the system are there for demonstration use only. They will NOT be embedded into any pdfs.