/// <summary>
    /// 添加傾斜水印
    /// </summary>
    /// <param name="pdfStream">pdf文件流</param>
    /// <param name="waterMarkName">水印字符串</param>
    /// <param name="width">頁面寬度</param>
    /// <param name="height">頁面高度</param>
    public MemoryStream SetWaterMark(MemoryStream pdfStream, string waterMarkName, float width, float height)
    {
      try
      {
        int fontSize = 50;//設(shè)置字體大小
        int span = 40;//設(shè)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);//華文云彩字體
        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);//在內(nèi)容上方加水印
                              //content = pdfStamper.GetUnderContent(i);//在內(nèi)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);//垂直重復(fù)的次數(shù)，進(jìn)一發(fā)
          int panleWith = (fontSize + span) * waterMarkNameLenth;
          int widthNumber = (int)Math.Ceiling((decimal)width / (decimal)panleWith);//水平重復(fù)次數(shù)
          
          // 設(shè)置水印文字字體傾斜 開始 
          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設(shè)置水印開始的絕對左邊，以左下角為x，y軸的起點(diǎn)
              for (int k = 0; k < waterMarkNameLenth; k++)
              {
                content.SetTextRise(yleng);//指定的y軸值處添加
                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;
      }
    }