Modify the RBuilder\Demos\EndUser\ReportExplorer example to do this as shown below:

{---------------------------------------------------------------------------}
{ TmyEndUserSolution.LoadEndEvent }

procedure TmyEndUserSolution.LoadEndEvent(Sender: TObject);
begin
  ppReport1.OnPreviewFormCreate := PreviewFormCreateEvent;
  ppReport1.OnPrintDialogCreate := PrintDialogCreateEvent;
end; {procedure, LoadEndEvent}


{---------------------------------------------------------------------------}
{ TmyEndUserSolution.PrintDialogCreateEvent }

procedure TmyEndUserSolution.PrintDialogCreateEvent(Sender: TObject);
begin

  ppReport1.PrintDialog.AllowPrintToFile := True;

  ppReport1.PrintDialog.TextFileName := 'c:\myReport.txt';
  ppReport1.PrintDialog.DeviceType := dtReportTextFile;

end;