procedure TForm1.Button1Click(Sender: TObject);
var
  BMP: TBitmap;
begin
  BMP:=TBitmap.Create;
  BMP.Height:=Form1.Height;
  BMP.Width:=Form1.Width;
  BMP.Canvas.CopyRect(BMP.Canvas.ClipRect, Form1.Canvas, Form1.Canvas.ClipRect);
  BMP.SaveToFile('C:\bmp.bmp');
  BMP.Free;
end;