getting error Document has no page when convert into pdf

Question

Hi

I am using .net bind my data into gridview and wanted to convert grid data into pdf file.

but occure a error like Document has no page . My code is bellow .

<form id="form1" runat="server">
<div>
<asp:GridView ID="GridView1" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
RowStyle-BackColor="#A1DCF2" AlternatingRowStyle-BackColor="White" AlternatingRowStyle-ForeColor="#000"
runat="server" AutoGenerateColumns="false" OnPageIndexChanging="OnPageIndexChanging">
</asp:GridView>
<br />
<asp:Button ID="btnExport" runat="server" Text="Export To PDF" OnClick = "ExportToPDF" />
</div>
</form>

Private Sub BindGrid()
Dim strConnString As String = ConfigurationManager.ConnectionStrings("safe").ConnectionString
Using con As New SqlConnection(strConnString)
Using cmd As New SqlCommand("select * from StudentDetails ")
Using sda As New SqlDataAdapter()
cmd.Connection = con
sda.SelectCommand = cmd
Using dt As New DataTable()
sda.Fill(dt)
GridView1.DataSource = dt
GridView1.DataBind()
End Using
End Using
End Using
End Using
End Sub
Protected Sub ExportToPDF(sender As Object, e As EventArgs) Handles btnExport.Click
Using sw As New StringWriter()
Using hw As New HtmlTextWriter(sw)
'To Export all pages
GridView1.AllowPaging = False
Me.BindGrid()
GridView1.RenderControl(hw)
Dim sr As New StringReader(sw.ToString())
'Dim pdfDoc As New Document(PageSize.A2, 10.0F, 10.0F, 10.0F, 0.0F)
Dim pdfdoc1 As New Document(PageSize.A4, 2.0F, 2.0F, 2.0F, 0.0F)
Dim htmlparser As New HTMLWorker(pdfdoc1)
PdfWriter.GetInstance(pdfdoc1, Response.OutputStream)
pdfdoc1.Open()
pdfdoc1.NewPage()
htmlparser.Parse(sr)
pdfdoc1.Close()
Response.ContentType = "application/pdf"
Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.pdf")
Response.Cache.SetCacheability(HttpCacheability.NoCache)
Response.Write(pdfdoc1)
Response.[End]()
End Using
End Using
End Sub
Protected Sub OnPageIndexChanging(sender As Object, e As GridViewPageEventArgs) Handles GridView1.PageIndexChanging
GridView1.PageIndex = e.NewPageIndex
Me.BindGrid()
End Sub
Public Overrides Sub VerifyRenderingInServerForm(ByVal control As Control)
End Sub

Can any one help me to solve this error.