Control 'MainContent_GridView1' of type 'GridView' must be placed inside a form tag with runat=server

Question

I have added iTextSharp to "Project>...Add References" and added them to using:

using iTextSharp.text;
using iTextSharp.text.html.simpleparser;
using iTextSharp.text.pdf;

I get the error code at line "GridView1.RenderControl(hw);".

How do you add a runat="server" thru Gridview and the HtmlTextWriter:

 Control 'MainContent_GridView1' of type 'GridView' must be placed inside a form tag with runat=server.

Button1_Click Code:

protected void Button1_Click(Object sender,System.EventArgs e)
    {
        string connStr = ConfigurationManager.ConnectionStrings["PDFMDF"].ConnectionString;
        DataSet ds = new DataSet();
        try
        {
            string cmdStr = "SELECT * FROM [GridviewTable];";
            using (SqlConnection conn = new SqlConnection(connStr))
            {
                using (SqlCommand cmd = new SqlCommand(cmdStr, conn))
                {
                    conn.Open();
                    using (SqlDataAdapter da = new SqlDataAdapter(cmd))
                    {
                        da.Fill(ds);
                        GridView1.DataSource = ds;
                        GridView1.DataBind();
                    }
                    conn.Close();
                    cmd.Dispose();
                    conn.Dispose();
                }
            }
        }
        catch  (Exception ex)
        {
            TextBox1.Text = ex.ToString();
        }

        Response.ContentType = "application/pdf";
        Response.AddHeader("content-disposition", "attachment;filename=this.pdf");
        Response.Cache.SetCacheability(HttpCacheability.NoCache);
        StringWriter sw = new StringWriter();
        HtmlTextWriter hw = new HtmlTextWriter(sw);
        GridView1.AllowPaging = false;
        GridView1.RenderControl(hw);
        StringReader sr = new StringReader(sw.ToString());
        Document PDFdoc = new Document(PageSize.A4, 10.0F, 10.0F, 10.0F, 0.0F);
        iTextSharp.text.html.simpleparser.HTMLWorker htmlparser =   new iTextSharp.text.html.simpleparser.HTMLWorker(PDFdoc);
        PdfWriter.GetInstance(PDFdoc, Response.OutputStream);
        PDFdoc.Open();
        htmlparser.Parse(sr);
        PDFdoc.Close();
        Response.Write(PDFdoc);
        Response.End();
    }

Answer 1

You can do this in your markup code. Ex.

 <asp:GridView ID="GridView1" runat="server">

Answer 2

in my markup allready have code runat="server" add this code to your source

    public override void VerifyRenderingInServerForm(Control control)
    {
        return;
    }

it solving the problem