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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