When you print a content add-in, an exact screenshot of the add-in’s current view is getting printed. This is unfavorable as all the UI/control elements you may use in your add-in (menus, buttons, navigation, etc.) get printed as well.

It would be so much better if Office could use the “screen” and “print” media types of CSS so you can hide specific elements (i.e. the UI ones) for the print-only appearance.