NSData CreatePDF (string text, float w, float h)
        {
            NSMutableData data = new NSMutableData ();
            UIGraphics.BeginPDFContext (data, new RectangleF (0, 0, w, h), null);
            UIGraphics.BeginPDFPage ();
            CGContext gctx = UIGraphics.GetCurrentContext ();

            //how to draw the text here?

            UIGraphics.EndPDFContent ();
            return data;
        }