ScriptManager Javascript response While Download file

1.Create a cookie before writing the stream to Response. 
2.Use JavaScript timer to check whether the value of cookie is set to true
3.If downloaded cookie is true, display a message that file download is successful and erase cookie

<script>
    var timer;
    function getCookie(name) {
        var re = new RegExp(name + "=([^;]+)");
        var value = re.exec(document.cookie);
        return (value != null) ? unescape(value[1]) : null;
    }
    function eraseCookie(name) {
        document.cookie = name + '=; expires=Thu, 01-Jan-70 00:00:01 GMT;';
    }
    function checkDownloadStatus() {
        var isDownloaded = getCookie("downloaded");
        //check if downloaded cookie value is true
        if (isDownloaded == 'true') {
            downloadedmessage.innerHTML = "File successfully downloaded";
            clearInterval(timer);
            //remove cookie
            eraseCookie("downloaded");
        }
    }
    function downloadButtonClick() {
        downloadedmessage.innerHTML = 'Please wait while your file is being downloaded';
        //check status every 300ms
        timer = setInterval(checkDownloadStatus, 300);
        return true;
    }
</script>

<form id="form1" runat="server">
    <asp:Button Text="Download File" ID="btnDownload" runat="server" OnClick="btnDownload_Click" OnClientClick="return downloadButtonClick();" />
    <div id="downloadedmessage" style="font-family: Tahoma; font-size: small;">
    </div>
</form>

protected void btnDownload_Click(object sender, EventArgs e)
{
    Byte[] bytes = File.ReadAllBytes(@"c:\\printdocument.pdf");
    Response.AddHeader("Content-Disposition", "attachment; filename=" + "print.pdf");            
    Response.ContentType = "application/pdf";
    //set cookie for tracking download status
    HttpCookie myCookie = new HttpCookie("downloaded");
    myCookie.Value = "true";
    myCookie.Expires = DateTime.Now.AddDays(1d);
    Response.Cookies.Add(myCookie);
    //simulate download wait
    System.Threading.Thread.Sleep(5000);
    Response.BinaryWrite(bytes.ToArray());
    Response.End();            
}