static void Main()
{
var pdf = new CGContextPDF(NSUrl.FromFilename("demo.pdf"), new RectangleF(0, 0, 617, 792));
pdf.BeginPage(null);
pdf.SetRGBFillColor(1, 0, 0, 1);
pdf.AddArc(300, 300, 100, 0, (float)(2 * Math.PI), true);
pdf.FillPath();
pdf.EndPage();
pdf.Flush();
}