I want to show logo retrieve from database as watermark in the background of the pdf page. It should be like this

        Response.ContentType = "application/pdf";
        Response.AddHeader("content-disposition", "attachment;filename=Report-StuExamResultCard-"+txtAdNo.Text.Trim()+".pdf");
        Response.Cache.SetCacheability(HttpCacheability.NoCache);

        string imageFilePath = @"C:\Reports\logo.jpg";
        iTextSharp.text.Image jpg = iTextSharp.text.Image.GetInstance(imageFilePath);
        jpg.ScaleToFit(375, 700);
        jpg.Alignment = iTextSharp.text.Image.UNDERLYING;
        jpg.SetAbsolutePosition(100, 400);
        Document doc = new Document(PageSize.A4);
        try
        {
             
            PdfWriter writer = PdfWriter.GetInstance(doc, Response.OutputStream);
            doc.Open();
            doc.NewPage();
            doc.Add(jpg);
            PdfPTable table = new PdfPTable(8);
            table.DefaultCell.Padding = 10f;
            table.DefaultCell.BackgroundColor = iTextSharp.text.Color.WHITE;
            table.DefaultCell.BorderColor = new iTextSharp.text.Color(191, 208, 247);
            table.HorizontalAlignment = Element.ALIGN_CENTER;
            table.DefaultCell.HorizontalAlignment = 1;
            table.TotalWidth = 500f;
            table.LockedWidth = true;
            table.AddCell(new Phrase(si, FontFactory.GetFont(FontFactory.HELVETICA_BOLD, 8)));
                table.AddCell(new Phrase(Subject, FontFactory.GetFont(FontFactory.HELVETICA_BOLD, 8)));
                table.AddCell(new Phrase(Totall, FontFactory.GetFont(FontFactory.HELVETICA_BOLD, 8)));
                table.AddCell(new Phrase(Obtained, FontFactory.GetFont(FontFactory.HELVETICA_BOLD, 8)));
                table.AddCell(new Phrase(Per, FontFactory.GetFont(FontFactory.HELVETICA_BOLD, 8)));
                table.AddCell(new Phrase(sgrade, FontFactory.GetFont(FontFactory.HELVETICA_BOLD, 8)));
                table.AddCell(new Phrase(sposition, FontFactory.GetFont(FontFactory.HELVETICA_BOLD, 8)));
                table.AddCell(new Phrase(sremarks, FontFactory.GetFont(FontFactory.HELVETICA_BOLD, 8)));
            doc.Close();
            Response.Write(doc);
            Response.End();
        }
        catch (Exception)
        {

            throw;
        }
        finally
        {
            doc.Close();
        }