how to retrieve arecord from database and show as pdf in iframe when dropdown box is selected

using System;
using System.Collections.Generic;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data;
using System.Data.SqlClient;
using System.IO;
using iTextSharp.text;
using iTextSharp.text.pdf;
using iTextSharp.text.html;
using iTextSharp.text.html.simpleparser;
using System.Text;
//using System.Data.SqlClient;
using System.Net;

public partial class dropdown_to_gridview : System.Web.UI.Page
{
   
    protected void Page_Load(object sender, EventArgs e)
    {
    
    }
    public void GridViewBind()
    {
        string cs = "Data Source=HOME;Initial Catalog=Registration;Integrated Security=True";
        SqlConnection con = new SqlConnection(cs);
        SqlCommand cmd = new SqlCommand("select * from employeep where Salary ='" + DropDownList1.SelectedValue + "'", con);
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataSet ds = new DataSet();
        da.Fill(ds);
        GridView1.DataSource = ds;
        GridView1.DataBind();
    }
    protected void btnExportPDF_Click(object sender, EventArgs e)
    {
        string cs = "Data Source=HOME;Initial Catalog=Registration;Integrated Security=True";
        SqlConnection con = new SqlConnection(cs);
        SqlCommand cmd = new SqlCommand("select * from employeep where Salary ='" + DropDownList1.SelectedValue + "'", con);
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataSet ds = new DataSet();
        da.Fill(ds);
        GridView1.DataSource = ds;
        GridView1.DataBind();
        
        Response.ContentType = "application/pdf";
        Response.AddHeader("content-disposition",
            "attachment;filename=report.pdf");
        Response.Cache.SetCacheability(HttpCacheability.NoCache);
        StringWriter sw = new StringWriter();
        HtmlTextWriter hw = new HtmlTextWriter(sw);
        GridView1.RenderControl(hw);
        StringReader sr = new StringReader(sw.ToString());
        Document pdfDoc = new Document(PageSize.A4, 10f, 10f, 10f, 0f);
        HTMLWorker htmlparser = new HTMLWorker(pdfDoc);
        PdfWriter.GetInstance(pdfDoc, Response.OutputStream);
        pdfDoc.Open();
        htmlparser.Parse(sr);
        pdfDoc.Close();
        Response.Write(pdfDoc);
        Response.End();
        pdfFrame.Attributes.Add("sr", "pdfDoc");
    }
    public override void VerifyRenderingInServerForm(Control control)
    {
        /* Verifies that the control is rendered */
    }
   
}