function ControlToBitmap(AControl: TWinControl): TBitmap;
begin
  Result := TBitmap.Create;
  with Result do begin
    Height := AControl.Height;
    Width  := AControl.Width;
    Canvas.Handle := CreateDC(nil, nil, nil, nil);
    Canvas.Lock;
    AControl.PaintTo(Canvas.Handle, 0, 0);
    Canvas.Unlock;
    DeleteDC(Canvas.Handle);
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  ImageEnView1.Bitmap.Assign(ControlToBitmap(ImageEnMView1));
  ImageEnView1.Bitmap.PixelFormat := pf24bit;
  ImageEnView1.Update;
end;

procedure TForm1.PrintCaptured1Click(Sender: TObject);
begin
  ImageEnView1.IO.DoPrintPreviewDialog(iedtDialog, 'Captured thumbanils', False, 'MyThumbnails');
end;