At the moment for medium trust support you can load fonts from a directory such as,
FontSettings.FontsBaseDirectory = Server.MapPath("Fonts/");
It would be great if you could support loading a custom font that is embedded as a resource in a DLL. As there are some low trust environments where you have no disk access at all.
Mario at GemBox
This feature request has been implemented and is available in the latest versions of GemBox.Document.