It's nowhere specified what fonts are installed within the application although on the official website, I've seen a section where users can buy fonts, therefore I don't think it has that many.
You won't have the possibility to add custom fonts, since they have to be especially created for Bookami, but that doesn't mean you can't try. Go to Start > Run > Fonts and drag and drop the fonts you have into that window.
Start Bookami to see if you can select the installed font.
