ExportToHttpResponse with AsyncPostBackTriggerin update panel not working

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C#

ASP.NET

// html code

<asp:UpdatePanel ID="up1" runat="server" >
                              <Triggers>
                                     <%-- <asp:AsyncPostBackTrigger ControlID ="linkbtnPDF" EventName="Click" /> --%>
                                  <asp:PostBackTrigger ControlID ="linkbtnPDF" />
                              </Triggers>
                             <%-- <asp:AsyncPostBackTrigger ControlID ="linkbtnPDF" EventName="Click" /> --%>



                             <ContentTemplate>
                              <asp:LinkButton ID="linkbtnPDF" runat="server" OnClick="linkbtnPDF_Click" >Pdf Export</asp:LinkButton>

                                 </ContentTemplate>
                         </asp:UpdatePanel>

<asp:UpdateProgress ID="Up4" runat="server" AssociatedUpdatePanelID="up1">
                         <ProgressTemplate>
                             <div class="model">
                                 <div class="center">
                                     <img id="progressimg" style="width:100%"  src="Images/progressbar4.gif" />
                                     </div>
                                 </div>
                             </ProgressTemplate>
                             </asp:UpdateProgress>

//c# code


ReportDocument rep = (ReportDocument)Session["reportdocument"];

Response.Buffer = false;

Response.ClearContent();
Response.ClearHeaders();

try
{


rep.ExportToHttpResponse(ExportFormatType.PortableDocFormat, Response, true, "Customers");

}
//catch (ThreadAbortException ex)
{
Response.Flush();





ex.Message.ToString();

finally
{
Response.End();
}


//please help me regarding progressbar exporting in pdf in updatepanel