Document has no pages

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C#3.5

Gridview

PDF

I am trying to export GridView data to PDF and I encountered with Document has no pages. I have 3 GridViews in a page and based on the visibility of the GridView I need to export the data to PDF. I searched on google and some articles on code project but none of them helped me. Please look into my code and help me with this problem. Below is the code :

Response.ContentType = "application/pdf";
            Response.AddHeader("content-disposition", "attachment;filename=UserDetails.pdf");
            Response.Cache.SetCacheability(HttpCacheability.NoCache);
            StringWriter sw = new StringWriter();
            HtmlTextWriter hw = new HtmlTextWriter(sw);
            GridView3.DataBind();
            GridView3.RenderControl(hw);
            GridView3.HeaderRow.Style.Add("width", "15%");
            GridView3.HeaderRow.Style.Add("font-size", "10px");
            GridView3.Style.Add("text-decoration", "none");
            GridView3.Style.Add("font-family", "Arial, Helvetica, sans-serif;");
            GridView3.Style.Add("font-size", "8px");
            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();

Thank You