private void DrawBottomFrame(PdfAppearance app)
{
app.MoveTo(borderWidth, borderWidth);
app.LineTo(box.Width - borderWidth, borderWidth);
app.LineTo(box.Width - borderWidth, box.Height - borderWidth);
app.LineTo(box.Width - 2 * borderWidth, box.Height - 2 * borderWidth);
app.LineTo(box.Width - 2 * borderWidth, 2 * borderWidth);
app.LineTo(2 * borderWidth, 2 * borderWidth);
app.LineTo(borderWidth, borderWidth);
app.Fill();
}