In DO#11 the 2009-vintage RTF viewer/editor is great; in DO#12 Microsoft Office 2007 'works' except there's no toolbar, and the legacy option (Office 2003) for DO#12 has a usable right-click menu but soft-crashes "docsvw.exe" (or whatever) every time you close the viewer panel. Do I need a later version of Office?
If you want an RTF viewer, either the one which comes with MS Word or the one that's built in to Windows should work fine. If both are installed you can pick which is used via Preferences / Viewer / Plugins and configuring the ActiveX + Preview + Office + Web plugin.
I don't know of any modern RTF editor that works as a preview handler or similar.
The Legacy Office option is best ignored and is not a good choice unless there is no alternative, due to the way Office is written.