C# 如何把画在picture控件图形保存为PDF格式的文件

C# 怎么把画在picture控件图形保存为PDF格式的文件
新做的一个绘图软件，需要在上面加上将图形保存为PDF格式。求指教
[解决办法]
用iTextSharp

 Document document = null;

            PdfWriter writer = null;
            string fileSavePath = "d:\";
            System.Drawing.Image sourceImg = null;

            iTextSharp.text.Image pdfImage = null;

            try
            {
             //   filePath = fileSavePath + "\temp" +  ".pdf";
                filePath = @"d:\temp.pdf";
                iTextSharp.text.Rectangle rectPageSize = new iTextSharp.text.Rectangle(PageSize.A4);

             //   rectPageSize = rectPageSize.Rotate();

                document = new Document(rectPageSize, 0, 0, 0, 0);

                writer = PdfWriter.GetInstance(document, new FileStream(filePath, FileMode.Create));

                document.Open();

            //    sourceImg = System.Drawing.Image.FromFile(fileSavePath + "\" + fileInputName);
                sourceImg =System.Drawing.Image.FromFile( fileInputName);
                pdfImage = iTextSharp.text.Image.GetInstance(sourceImg, GetImageFormat(GetFileExtendName(fileInputName))); 
 

                pdfImage.Alignment = iTextSharp.text.Image.ALIGN_CENTER;

                float height = document.Top - document.TopMargin;
                //图片原始大小
                pdfImage.ScaleToFit(sourceImg.Width > document.Right ? document.Right : sourceImg.Width, sourceImg.Height > height ? height : sourceImg.Height);

                //pdfImage.ScaleToFit(document.Right ,height);

                document.Add(pdfImage);
                document.NewPage();
                sourceImg = System.Drawing.Image.FromFile("2.jpg");
                pdfImage = iTextSharp.text.Image.GetInstance(sourceImg, GetImageFormat(GetFileExtendName("2.jpg")));
                pdfImage.Alignment = iTextSharp.text.Image.ALIGN_CENTER;
                pdfImage.ScaleToFit(sourceImg.Width > document.Right ? document.Right : sourceImg.Width, sourceImg.Height > height ? height : sourceImg.Height);
                document.Add(pdfImage);
                
                sourceImg = null;

                pdfImage = null;

                document.Close();

                writer.Close();