Thanks for writing in! With the latest version of the theme Pro 1.2.7/X 5.2.5, you can insert a custom font by going to X/Pro > Launch > Templates > Fonts.
At the moment, you are only allowed to insert typekit fonts. Uploading your own custom font is not yet available. We've added this as a feature request so it can be taken into consideration for future development.
Thank you for your understanding.