Displaying RTF documents: Is it possible to view RTF files with the Controls component?
Yes, this is possible. Example:

GuiXT script:

Control (1,1) (25,145) name="rtf" progid="RICHTEXT.RichtextCtrl"
initflag="rtfnew"

if V[rtfnew]
   CallVbs set_rtf_content "&V[rtf]"
endif

VBScript:

Function set_rtf_content(objRTF)
    Call objRTF.LoadFile("S:\scripts\sample.invoice.rtf")
  End Function

Instead of loading the rtf document from a file you may use a GuiXT long text variable that contains the RTF text.