var
  pbRect: TRect;
begin
  pbRect := Rect(0, 0, PaintBox1.Width, PaintBox1.Height);
  BitMap := TBitMap.Create;
  try
    Bitmap.Width := PaintBox1.Width;
    Bitmap.Height := PaintBox1.Height;
    BitMap.Canvas.CopyRect(pbRect, PaintBox1.Canvas, pbRect);
    ClipBoard.Assign(BitMap);
  finally
    BitMap.Free;
  end;
end;