Download with c# and rename file

 string strURL=txtFileName.Text;
        WebClient req=new WebClient();
        HttpResponse response = HttpContext.Current.Response;
        response.Clear();
        response.ClearContent();
        response.ClearHeaders();
        response.Buffer= true;
        response.AddHeader("Content-Disposition","attachment;filename=\"" + Server.MapPath(strURL) + "\"");
        byte[] data=req.DownloadData(Server.MapPath(strURL));
        response.BinaryWrite(data);
        response.End();