iTextSharp给PDF添加水印

  #region 每页加公章
                    string AreaCode = UnitInfoQueryBll.Instance.getAreaCode(currentUser.UINTID);
                    if (!string.IsNullOrEmpty(AreaCode))
                    {
                        int pages = document.PageNumber;
                        PdfReader reader = new PdfReader(HttpContextHelper.AppRootPath + pdfpath + pdfName + ".pdf");
                        int n = reader.NumberOfPages;
                        PdfStamper stamper = new PdfStamper(reader, new FileStream(HttpContextHelper.AppRootPath + pdfpath + pdfName + "a.pdf", FileMode.Create));
                        int j = 0;
                        PdfContentByte contentByte;
                        iTextSharp.text.Image img = iTextSharp.text.Image.GetInstance(imgePath + AreaCode + ".png");
                        img.ScalePercent(75f);
                        img.SetAbsolutePosition(300, 550);
                        while (j < n)
                        {
                            j++;
                            contentByte= stamper.GetOverContent(j);
                            contentByte.AddImage(img);
                        }
                        stamper.Close();
                        reader.Close();

                    }
   #endregion