在现有PDF文件上添加水印

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using iTextSharp.text.html.simpleparser;
using iTextSharp.text.pdf;
using iTextSharp.text;
using System.IO;
using System.Web.UI.HtmlControls;
using System.Drawing;

//itextsharp.dll version:5.1.10

protected void Button1_Click(object sender, EventArgs e)
     {
        string source =@"D:\My.Sample\C#NET\Exoport2PDF\Web2\Chap1011.pdf"; //模板路径
        string output = @"D:\My.Sample\C#NET\Exoport2PDF\Web2\Chap1012.pdf"; //导出水印背景后的PDF
        string watermark = @"D:\My.Sample\C#NET\Exoport2PDF\Web2\gp0.jpg";   // 水印图片

        bool isSurrcess = PDFWatermark(source, output, watermark, 10, 10);
        
     }


    public  bool PDFWatermark(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(1);

            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 = 20;//透明度，灰色填充
            //image.Rotation//旋转
            //image.RotationDegrees//旋转角度
            //水印的位置 
            if (left < 0)
            {
                left = width - image.Width + left;
            }

            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 = 1; i <= numberOfPages; i++)
            {
                waterMarkContent = pdfStamper.GetUnderContent(i);

                waterMarkContent.AddImage(image);
            }
            //strMsg = "success";
            return true;
        }
        catch (Exception ex)
        {
             ex.Message.Trim();
            return false;
        }
        finally
        {

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

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