PDF加水印

using System.IO;

using iTextSharp.text;
using iTextSharp.text.pdf;

/// <summary>
        ///  PDF加水印
        /// </summary>
        /// <param name="inputfilepath">源PDF文件</param>
        /// <param name="outputfilepath">加水印后PDF文件 </param>
        /// <param name="ModelPicName">水印文件路径</param>
        /// <param name="top">离顶部距离</param>
        /// <param name="left">离左边距离,如果为负,则为离右边距离</param>
        /// <param name="strMsg">返回信息</param>
        /// <returns>返回</returns>
        public static bool PDFWatermark(string inputfilepath, string outputfilepath, string ModelPicName, float top, float left, ref string strMsg)
        {
            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)
            {
                strMsg = ex.Message.Trim();
                return false;
            }
            finally
            {

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

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