The only fonts available in FormsCentral, are the ones listed in the Font menu by default--there is no way to add fonts to that menu. Please see this explanation from a similar post:
"The fonts we offer are web-safe fonts meaning that they can be displayed the same way on any web browser (any machine, device, OS...). The fonts that you have on your computer might not be available on your filler's machine when the are filling up your form. The form would look good on your machine but not on your filler's machine or device."