复制网上代码，gridview导出PDF后打开异常

        Response.ContentType = "application/pdf";        Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.pdf");        Response.Cache.SetCacheability(HttpCacheability.NoCache);        StringWriter sw = new StringWriter();        HtmlTextWriter hw = new HtmlTextWriter(sw);        GridView1.AllowPaging = false;        GridView1.DataBind();        GridView1.RenderControl(hw);        StringReader sr = new StringReader(sw.ToString());        Document pdfDoc = new Document(PageSize.A4, 10f, 10f, 10f, 10f);        HTMLWorker htmlparser = new HTMLWorker(pdfDoc);        PdfWriter.GetInstance(pdfDoc, Response.OutputStream);        // pdfDoc.Open();        htmlparser.Parse(sr);        // pdfDoc.Close();        Response.Write(pdfDoc);        Response.End();