Code:
function ShowRTF(RE: TRichedit): string;
var
   strStream: TStringStream;
begin
   strStream := TStringStream.Create('') ;
   try
     RE.PlainText := False;
     RE.Lines.SaveToStream(strStream) ;
     Result := strStream.DataString;
   finally
     strStream.Free
   end;
end;

Memo1.Text:= ShowRTF(RichEdit1);