Export GridView to PDF/Excel in asp .net.

 public override void VerifyRenderingInServerForm(Control control) { }
    protected void btnConvertpdf_Click(object sender, EventArgs e)
    {
        #region pdf
        Response.ContentType = "application/pdf";
        Response.AddHeader("content-disposition", "attachment;filename=BRS.pdf");
        Response.Cache.SetCacheability(HttpCacheability.NoCache);
        StringWriter sw = new StringWriter();
        HtmlTextWriter hw = new HtmlTextWriter(sw);
        gridviewid.AllowPaging = false;
        gridviewid.DataBind();
        gridviewid.RenderControl(hw);
        StringReader sr = new StringReader(sw.ToString());
        Document pdfDoc = new Document(PageSize.A2, 7f, 7f, 7f, 0f);
        HTMLWorker htmlparser = new HTMLWorker(pdfDoc);
        PdfWriter.GetInstance(pdfDoc, Response.OutputStream);
        pdfDoc.Open();
        htmlparser.Parse(sr); pdfDoc.Close();
        Response.Write(pdfDoc);
        Response.End();
        #endregion
    }
    protected void btnConvertexcel_Click(object sender, EventArgs e)
    {
     
        Response.ClearContent();
        Response.Buffer = true;
        Response.AddHeader("content-disposition", string.Format("attachment; filename={0}", "BRS.xls"));
        Response.ContentType = "application/ms-excel";
        StringWriter sw = new StringWriter();
        HtmlTextWriter htw = new HtmlTextWriter(sw);
        gridviewid.AllowPaging = false; gridviewid.DataBind();
        gridviewid.HeaderRow.Style.Add("background-color", "#FFFFFF");
        gridviewid.RenderControl(htw);
        Response.Write(sw.ToString());
        Response.End();
    }

Note: itextshrp.dll shoul be used and page event validation should be false
using iTextSharp.text;
using iTextSharp.text.html.simpleparser;
using iTextSharp.text.pdf;
using System.Web.UI.WebControls;
(EnableEventValidation = "false" )