C#向pdf 添加水印

 调用直接这样用：
  //PDFHelper.AddImageWatermarkPDF(path, "D://my.pdf", Server.MapPath("/HtmlToPdf/Tools/sy.bmp"), 0, 0);
             string temp = DateTime.Now.ToLongDateString() + "  " + DateTime.Now.ToLongTimeString();
             Guid guid = new Guid();
             guid = Guid.NewGuid();

             string tempGUID = guid.ToString();
             File.Copy("E:\\1.pdf", "E:\\11.pdf", true);
             PDFHelper.AddWordWatermark2PDF("E:\\11.pdf", "E:\\1.pdf", "西安咸阳国际机场南三指廊航站楼工程施工及施工管理总承包" + "_" + temp + "_" + tempGUID + "_7.1");
             //PDFSetWaterMark.setWatermark("D://my.pdf", "D://my2.pdf", "TEST", "", "", 1);

 using iTextSharp.text;
 using iTextSharp.text.pdf;
 using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;

 namespace Test测试
 {
     public static class PDFHelper
     {

         /// <summary>
         /// 加图片水印
         /// </summary>
         /// <param name="inputfilepath"></param>
         /// <param name="outputfilepath"></param>
         /// <param name="ModelPicName"></param>
         /// <param name="top"></param>
         /// <param name="left"></param>
         /// <returns></returns>
         public static bool AddImageWatermarkPDF(string inputfilepath, string outputfilepath, string ModelPicName, float top, float left)
         {
             //throw new NotImplementedException();
             PdfReader pdfReader = null;
             PdfStamper pdfStamper = null;
             try
             {
                 pdfReader = new PdfReader(inputfilepath);

                 int numberOfPages = pdfReader.NumberOfPages;

                 iTextSharp.text.Rectangle psize = pdfReader.GetPageSize();

                 float width = psize.Width;

                 float height = psize.Height;

                 pdfStamper = new PdfStamper(pdfReader, new FileStream(outputfilepath, FileMode.Create));

                 PdfContentByte waterMarkContent;

                 iTextSharp.text.Image image = iTextSharp.text.Image.GetInstance(ModelPicName);

                 image.GrayFill = ;//透明度，灰色填充
                                     //image.Rotation//旋转
                                     //image.RotationDegrees//旋转角度
                                     //水印的位置
                 if (left < )
                 {
                     left = width /  - image.Width + left;
                 }

                 //image.SetAbsolutePosition(left, (height - image.Height) - top);
                 image.SetAbsolutePosition(left, (height /  - image.Height) - top);

                 //每一页加水印,也可以设置某一页加水印
                 for (int i = ; i <= numberOfPages; i++)
                 {
                     //waterMarkContent = pdfStamper.GetUnderContent(i);//内容下层加水印
                     waterMarkContent = pdfStamper.GetOverContent(i);//内容上层加水印

                     waterMarkContent.AddImage(image);
                 }
                 //strMsg = "success";
                 return true;
             }
             catch (Exception ex)
             {
                 throw ex;

             }
             finally
             {

                 if (pdfStamper != null)
                     pdfStamper.Close();

                 if (pdfReader != null)
                     pdfReader.Close();
             }
         }
         /// <summary>
         /// 添加普通偏转角度文字水印
         /// </summary>
         /// <param name="inputfilepath"></param>
         /// <param name="outputfilepath"></param>
         /// <param name="waterMarkName"></param>
         /// <param name="permission"></param>
         public static void AddWordWatermark2PDF(string inputfilepath, string outputfilepath, string waterMarkName)
         {
             PdfReader pdfReader = null;
             PdfStamper pdfStamper = null;
             try
             {
                 pdfReader = new PdfReader(inputfilepath);
                 pdfStamper = new PdfStamper(pdfReader, new FileStream(outputfilepath, FileMode.Create));
                 int total = pdfReader.NumberOfPages + ;
                 iTextSharp.text.Rectangle psize = pdfReader.GetPageSize();
                 float width = psize.Width;
                 float height = psize.Height;
                 PdfContentByte content;
                 BaseFont font = BaseFont.CreateFont(@"C:\WINDOWS\Fonts\SIMFANG.TTF", BaseFont.IDENTITY_H, BaseFont.EMBEDDED);
                 PdfGState gs = new PdfGState();
                 for (int i = ; i < total; i++)
                 {
                     content = pdfStamper.GetOverContent(i);//在内容上方加水印
                     //content = pdfStamper.GetUnderContent(i);//在内容下方加水印
                     //透明度
                     gs.FillOpacity = 0.5f;
                     content.SetGState(gs);
                     content.SetGrayFill(0.5f);
                     //开始写入文本
                     content.BeginText();
                     //content.SetColorFill(BaseColor.LIGHT_GRAY);
                     //content.SetFontAndSize(font, 100);
                     //content.SetTextMatrix(0, 0);
                     //content.ShowTextAligned(Element.ALIGN_CENTER, waterMarkName, width / 2 - 50, height / 2 - 50, 55);
                     content.SetColorFill(BaseColor.GRAY);
                     content.SetFontAndSize(font, );
                     content.ShowTextAligned(Element.ALIGN_CENTER, waterMarkName, width /  - , height /  - , );
                     content.EndText();
                 }
             }
             catch (Exception ex)
             {
                 throw ex;
             }
             finally
             {

                 if (pdfStamper != null)
                     pdfStamper.Close();

                 if (pdfReader != null)
                     pdfReader.Close();
             }
         }

         /// <summary>
         /// 添加倾斜水印
         /// </summary>
         /// <param name="inputfilepath"></param>
         /// <param name="outputfilepath"></param>
         /// <param name="waterMarkName"></param>
         /// <param name="userPassWord"></param>
         /// <param name="ownerPassWord"></param>
         /// <param name="permission"></param>
         public static void setWatermark(string inputfilepath, string outputfilepath, string waterMarkName, string userPassWord, string ownerPassWord, int permission)
         {
             PdfReader pdfReader = null;
             PdfStamper pdfStamper = null;
             try
             {
                 pdfReader = new PdfReader(inputfilepath);
                 pdfStamper = new PdfStamper(pdfReader, new FileStream(outputfilepath, FileMode.Create));
                 // 设置密码
                 //pdfStamper.SetEncryption(false,userPassWord, ownerPassWord, permission);

                 int total = pdfReader.NumberOfPages + ;
                 PdfContentByte content;
                 BaseFont font = BaseFont.CreateFont(@"C:\WINDOWS\Fonts\SIMFANG.TTF", BaseFont.IDENTITY_H, BaseFont.EMBEDDED);
                 PdfGState gs = new PdfGState();
                 gs.FillOpacity = 0.2f;//透明度

                 int j = waterMarkName.Length;
                 char c;
                 int rise = ;
                 for (int i = ; i < total; i++)
                 {
                     rise = ;
                     content = pdfStamper.GetOverContent(i);//在内容上方加水印
                                                            //content = pdfStamper.GetUnderContent(i);//在内容下方加水印

                     content.BeginText();
                     content.SetColorFill(BaseColor.DARK_GRAY);
                     content.SetFontAndSize(font, );
                     // 设置水印文字字体倾斜 开始
                     if (j >= )
                     {
                         content.SetTextMatrix(, );
                         for (int k = ; k < j; k++)
                         {
                             content.SetTextRise(rise);
                             c = waterMarkName[k];
                             content.ShowText(c + "");
                             rise -= ;
                         }
                     }
                     else
                     {
                         content.SetTextMatrix(, );
                         for (int k = ; k < j; k++)
                         {
                             content.SetTextRise(rise);
                             c = waterMarkName[k];
                             content.ShowText(c + "");
                             rise -= ;
                         }
                     }
                     // 字体设置结束
                     content.EndText();
                     // 画一个圆
                     //content.Ellipse(250, 450, 350, 550);
                     //content.SetLineWidth(1f);
                     //content.Stroke();
                 }

             }
             catch (Exception ex)
             {
                 throw ex;
             }
             finally
             {

                 if (pdfStamper != null)
                     pdfStamper.Close();

                 if (pdfReader != null)
                     pdfReader.Close();
             }
         }

     }

 }