C#使用iTextSharp添加PDF水印

使用的是iTextSharp添加PDF水印，由于是接口动态生成PDF，所以采用的是全部是内存流的形式，而且水印是平铺是。iTextSharp版本是5.5。

/// <summary>
    /// 添加倾斜水印
    /// </summary>
    /// <param name="pdfStream">pdf文件流</param>
    /// <param name="waterMarkName">水印字符串</param>
    /// <param name="width">页面宽度</param>
    /// <param name="height">页面高度</param>
    public MemoryStream SetWaterMark(MemoryStream pdfStream, string waterMarkName, float width, float height)
    {
      try
      {
        int fontSize = 50;//设置字体大小
        int span = 40;//设置垂直位移
        MemoryStream outStream = new MemoryStream();
        PdfReader pdfReader = new PdfReader(pdfStream);
        PdfStamper pdfStamper = new PdfStamper(pdfReader, outStream);
        pdfStamper.Writer.CloseStream = false;
        int total = pdfReader.NumberOfPages + 1;
        PdfContentByte content;
        BaseFont font = BaseFont.CreateFont(@"C:\WINDOWS\Fonts\STCAIYUN.TTF", BaseFont.IDENTITY_H, BaseFont.EMBEDDED);//华文云彩字体
        PdfGState gs = new PdfGState();
        gs.FillOpacity = 0.15f;//透明度
        int waterMarkNameLenth = waterMarkName.Length;
        char c;
        int rise = 0;
        string spanString = " ";//水平位移
        for (int i = 1; i < total; i++)
        {
          rise = waterMarkNameLenth * span;
          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.SetGState(gs);
          content.BeginText();
          content.SetColorFill(BaseColor.GREEN);
          content.SetFontAndSize(font, fontSize);
          int heightNumbert = (int)Math.Ceiling((decimal)height / (decimal)rise);//垂直重复的次数，进一发
          int panleWith = (fontSize + span) * waterMarkNameLenth;
          int widthNumber = (int)Math.Ceiling((decimal)width / (decimal)panleWith);//水平重复次数
          
          // 设置水印文字字体倾斜 开始 
          for (int w = 0; w < widthNumber; w++)
          {
            for (int h = 1; h <= heightNumbert; h++)
            {
              int yleng = rise * h;
              content.SetTextMatrix(w * panleWith, yleng);//x,y设置水印开始的绝对左边，以左下角为x，y轴的起点
              for (int k = 0; k < waterMarkNameLenth; k++)
              {
                content.SetTextRise(yleng);//指定的y轴值处添加
                c = waterMarkName[k];
                content.ShowText(c + spanString);
                yleng -= span;
              }
            }
          }
          content.EndText();
        }
        if (pdfStamper != null)
          pdfStamper.Close();

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

        return outStream;
      }
      catch (Exception ex)
      {
        throw ex;
      }
    }

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