C# pdf 插入图片

PdfReader reader = new PdfReader(_txtPdf.Text);
            // 获得文档页数
            int n = reader.NumberOfPages;
            // 获得第一页的大小
            iTextSharp.text.Rectangle psize = reader.GetPageSize(1);
            float width = psize.Width;
            float height = psize.Height;
            iTextSharp.text.Document document = new iTextSharp.text.Document(psize, 30, 30, 30, 30);
            PdfWriter writer = PdfWriter.GetInstance(document,
                                     new FileStream(@"D:\Example\PdfFile\" + DateTime.Now.ToString("yyyyMMddHHmmss") + ".pdf", FileMode.Create));
            document.Open();
            PdfContentByte cb = writer.DirectContent;
            PdfImportedPage page1 = writer.GetImportedPage(reader, 1);
            cb.AddTemplate(page1, 0, 0);
            iTextSharp.text.Image img = iTextSharp.text.Image.GetInstance(_txtImg.Text);
            img.SetAbsolutePosition(Convert.ToInt32(_txtX.Text), height - Convert.ToInt32(_txtY.Text));
            cb.AddImage(img);
            writer.Flush();
            document.Close();