I don't know 'GroupDocs' I'm afraid - but looking at their website - it looks like they offer both a 'Fat Client' (based on Java by the look of it) - and a browser-embedded version (not clear to me how that is built - but I assume it's a HTML/JS/CSS type thing).
Have you figured out already how to get 'GroupDocs' working outside of PRPC (in a browser I mean) ?
If you have: then most probably I would guess you would want to look at something like this procedure:
1. Upload any CSS/JS scripts it is built on into PRPC.
You may also want to include some parameters on the control; so you can pass in arguments from a PRPC model etc. And you will probably (this is a guess) need to make use of Pega JSP Tags in order to interact with the GroupDocs HTML/JS/CSS (that is: refer to PRPC Property values etc).
I can't give any specifics here I'm afraid, since I'm not familiar with GroupDocs; maybe somebody else can help.