[Solved] Column Header not displaying while exporting DataTable to PDF using iTextSharp in ASP.Net

how can i add columnheader of datatable in pdf

i can't get column header

        protected void Button2_Click(object sender, EventArgs e)
        {
            string companyName = Session["branch"].ToString();
            int orderNo = 2303;
            DataTable dt = new DataTable();
            string constring = ConfigurationManager.ConnectionStrings["conn"].ConnectionString;
            using (SqlConnection con = new SqlConnection(constring))
            {
                using (SqlCommand cmd = new SqlCommand("SELECT sell.product_name as Product,sell.quantity,sell.price,sell.total_price FROM sell,customer where customer.id=sell.cid and sell.date='7/31/2019';", con))
                {
                    using (SqlDataAdapter sda = new SqlDataAdapter())
                    {
                        con.Open();
                        cmd.CommandType = CommandType.Text;
                        sda.SelectCommand = cmd;
                        sda.Fill(dt);
                        con.Close();
                    }
                }
            }
            using (StringWriter sw = new StringWriter())
            {
                using (HtmlTextWriter hw = new HtmlTextWriter(sw))
                {
                    StringBuilder sb = new StringBuilder();

                    //Generate Invoice (Bill) Header.
                    sb.Append("<table width='100%' cellspacing='0' cellpadding='2'>");
                    sb.Append("<tr><td align='center' style='background-color: #18B5F0' colspan = '2'><b>Order Sheet</b></td></tr>");
                    sb.Append("<tr><td colspan = '2'></td></tr>");
                    sb.Append("<tr><td><b>Order No: </b>");
                    sb.Append(orderNo);
                    sb.Append("</td><td align = 'right'><b>Date: </b>");
                    sb.Append(DateTime.Now);
                    sb.Append(" </td></tr>");
                    sb.Append("<tr><td colspan = '2'><b>Branch Name: </b>");
                    sb.Append(companyName);
                    sb.Append("</td></tr>");
                    sb.Append("</table>");
                    sb.Append("<br />");

                    //Generate Invoice (Bill) Items Grid.
                    sb.Append("<table border = '1'>");
                    sb.Append("<tr>");
                    foreach (DataColumn column in dt.Columns)
                    {
                        sb.Append("<th style = 'background-color: #D20B0C;color:#ffffff'>");
                        sb.Append(column.ColumnName);
                        sb.Append("</th>");
                    }
                    sb.Append("</tr>");
                    foreach (DataRow row in dt.Rows)
                    {
                        sb.Append("<tr>");
                        foreach (DataColumn column in dt.Columns)
                        {
                            sb.Append("<td>");
                            sb.Append(row[column]);
                            sb.Append("</td>");
                        }
                        sb.Append("</tr>");
                    }
                    sb.Append("<tr><td align = 'right' colspan = '");
                    sb.Append(dt.Columns.Count - 1);
                    sb.Append("'>Total</td>");
                    sb.Append("<td>");
                    sb.Append(dt.Compute("sum(total_price)", ""));
                    sb.Append("</td>");
                    sb.Append("</tr></table>");

                    //Export HTML String as PDF.
                    StringReader sr = new StringReader(sb.ToString());
                    Document pdfDoc = new Document(PageSize.A4, 10f, 10f, 10f, 0f);
                    HTMLWorker htmlparser = new HTMLWorker(pdfDoc);
                    PdfWriter writer = PdfWriter.GetInstance(pdfDoc, Response.OutputStream);
                    pdfDoc.Open();
                    htmlparser.Parse(sr);
                    pdfDoc.Close();
                    Response.ContentType = "application/pdf";
                    Response.AddHeader("content-disposition", "attachment;filename=Invoice_" + orderNo + ".pdf");
                    Response.Cache.SetCacheability(HttpCacheability.NoCache);
                    Response.Write(pdfDoc);
                    Response.End();
                }
            }