if (File.Exists(filepath))
                {
                    Workbook workbook = new Workbook();
                    workbook.LoadFromFile(filepath);
                    using (StreamWriter sw = new StreamWriter(logPath, true))
                    {
                        sw.WriteLine("文件存在:" + DateTime.Now.ToString()+","+ 　　　　　　　　　　　　　　 workbook.Worksheets.Count);
                    }
                    for (int j = 0; j < workbook.Worksheets.Count; j++)
                    {
                        Worksheet sheet = workbook.Worksheets[j];
                        string fileName = sheet.Name;
                        string OnlyCode = Guid.NewGuid().ToString();
                        string DocumentPath = savePath + OnlyCode + ".pdf";
                        string officePath = savePath + OnlyCode + "_1.pdf";

                        sheet.SaveToPdf(DocumentPath);
                        //sheet.Dispose();
                        AddImgToPdf(DocumentPath, officePath);增加图片到PDF
                    }
                    workbook.Dispose();
                }

protected void AddImgToPdf(string path, string toPath)
        {
            string imgUrl = @"C:\MES_Web\Images\official_seal.png";
            if (File.Exists(toPath))
                File.Delete(toPath);
            using (Stream inputPdfStream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read))
            using (Stream inputImageStream = new FileStream(imgUrl, FileMode.Open, FileAccess.Read, FileShare.Read))
            using (Stream outputPdfStream = new FileStream(toPath, FileMode.Create, FileAccess.Write, FileShare.None))
            {
                var reader = new PdfReader(inputPdfStream);
                var stamper = new PdfStamper(reader, outputPdfStream);
                var pdfContentByte = stamper.GetOverContent(1);

                iTextSharp.text.Image image = iTextSharp.text.Image.GetInstance(inputImageStream);
                image.SetAbsolutePosition(100, 100);
                pdfContentByte.AddImage(image);
                stamper.Close();
                stamper.Dispose();
            }
            File.Replace(toPath, path, path + ".back");
        }