errors in pdf file that contain gridview

See more:

C#

VS2010

i actually want to download pdf file that contain pid, and month from january to december. the month contain float number which has 9number after coma, so it makes the griedview wider than what it should be. and when i i download the pdf file, inside the file shows error 'System.Web.UI.HtmlTextWriter'

what is actually happen here??

below is my code

connection.Open();
    SqlCommand dm = new SqlCommand("select id,sum (case when [Month] = 1 then demand else 0.0 end) January, sum(case when [Month] = 2 then demand  else 0.0 end) February,sum(case when [Month] = 3 then demand  else 0.0 end) March ,sum(case when [Month] = 4 then demand  else 0.0 end) April ,sum(case when [Month] = 5 then demand  else 0.0 end) May ,sum(case when [Month] = 6 then demand  else 0.0 end) June ,sum(case when [Month] = 7 then demand  else 0.0 end) July ,sum(case when [Month] = 8 then demand  else 0.0 end) August ,sum(case when [Month] = 9 then demand  else 0.0 end) September ,sum(case when [Month] = 10 then demand  else 0.0 end) October ,sum(case when [Month] = 11 then demand  else 0.0 end) November ,sum(case when [Month] = 12 then demand  else 0.0 end) December from reorder group by id", connection);
    SqlDataReader fdm = dm.ExecuteReader();

    if (fdm.HasRows)
    {
        fdm.Read();
        GridView3.DataSource = fdm;

    }
    connection.Close();

    Response.ContentType = "application/pdf";
    Response.AddHeader("content-disposition", "attachment;filename=Demand.pdf");
    Response.Cache.SetCacheability(HttpCacheability.NoCache);
    StringWriter wsfdm = new StringWriter();
    HtmlTextWriter fdmws = new HtmlTextWriter(wsfdm);
    GridView3.AllowPaging = false;
    GridView3.RenderControl(fdmws);
    GridView3.HeaderRow.Style.Add("width", "20%");
    GridView3.HeaderRow.Style.Add("font-size", "8x");
    GridView3.Style.Add("text-decoration", "none");
    GridView3.Style.Add("font-family", "Arial, Helvetica, sans-serif;");
    GridView3.Style.Add("font-size", "8px");

    StringReader fgdm = new StringReader(fdmws.ToString());
    Document documentpdf = new Document(PageSize.A4, 10f, 10f, 10f, 0f);
    HTMLWorker htmlparser = new HTMLWorker(documentpdf);
    PdfWriter.GetInstance(documentpdf, Response.OutputStream);
    documentpdf.Open();
    htmlparser.Parse(fgdm);
    documentpdf.Close();
    Response.Write(documentpdf);
    Response.End();
}