// Add LOGO inside pdf
        string filename = Server.MapPath("~/Uploads/") + FileUpload1.FileName.ToString();
        FileUpload1.SaveAs(filename);
        PdfDocument document = PdfReader.Open(filename);
        // Set version to PDF 1.4 (Acrobat 5) because we use transparency.
        if (document.Version < 14)
            document.Version = 14;

        for (int idx = 0; idx < document.Pages.Count; idx++)
        {
            PdfPage page = document.Pages[idx];
            XGraphics gfx = XGraphics.FromPdfPage(page, XGraphicsPdfPageOptions.Prepend);

            string imgPath = System.Web.HttpContext.Current.Server.MapPath("Images/nals_logo.jpg");
            XImage image = XImage.FromFile(imgPath);
            gfx.DrawImage(image, 100, 200);
        }
        // Save the document...
        document.Save(filename);
        // ...and start a viewer
        Process.Start(filename);