Basically, you can use all the fonts installed on your computer in Purple DS Composer. However, in a Purple DS app only TrueType fonts (.ttf) can be displayed. Therefore before using fonts, you should check to see if the font is available as a TrueType font and confirm that you have the correct license to use.
We recommend that you use Google Fonts as it provides you with over 700 fonts in the .ttf format that are free to use.
For more information on how to integrate fonts into an app, click here.