If you are simply trying to play D&D 5e online, stop now and download Fantasy Grounds Unity. But if you are an archivist, a retro-gamer, or a tabletop historian wanting to run The Keep on the Shadowfell exactly as it was hosted on a laggy Hamachi connection in 2012—then fire up that old machine, follow the RH guide, and keep the server alive.
Once inside a game, go to the Library and then the Modules button to "open" the books you want to use. Version & Compatibility Note fantasy grounds ii v2012 extras rh install
Installing these add-ons usually requires manual placement in the application data folder. If you are simply trying to play D&D