Code:

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;