Code
  public class AutoDownload : IHttpHandler
    {

        #region IHttpHandler Members

        public bool IsReusable
        {
            get { return false; }
        }

        public void ProcessRequest(HttpContext context)
        {
            try
            {
                string fileName = SoFContext.Current.GetStringInQs("fn", string.Empty);
                string siteUrl= System.Configuration.ConfigurationManager.AppSettings["SiteUrl"].ToString();
                string user = System.Configuration.ConfigurationManager.AppSettings["FtpUser"].ToString();
                string passWord = System.Configuration.ConfigurationManager.AppSettings["FtpPassWord"].ToString();
                
                string filePath = string.Empty;
                 filePath = siteUrl+ fileName;
                
                string file = Path.GetFileName(filePath);

                HttpContext.Current.Response.Buffer = true;
                HttpContext.Current.Response.Charset = "utf-8";
                HttpContext.Current.Response.ContentEncoding = Encoding.UTF8;
                HttpContext.Current.Response.Clear();
                HttpContext.Current.Response.ContentType = "application/octet-stream";
                HttpContext.Current.Response.AppendHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(file, Encoding.UTF8));
   
             HttpWebRequest httpWebRequest;
                httpWebRequest = (HttpWebRequest)HttpWebRequest.Create(filePath);

                NetworkCredential credential;
                if (!string.IsNullOrEmpty(user) && !string.IsNullOrEmpty(passWord))
                {
                    credential = new NetworkCredential(user, passWord);
                    httpWebRequest.Credentials = credential;
                }
                
                using (HttpWebResponse httpWebResponse = (HttpWebResponse)httpWebRequest.GetResponse())
                {
                    using (Stream responseStream = httpWebResponse.GetResponseStream())
                    {

                        byte[] arrayByte;
                        byte[] buffer = new byte[4096];
                        using (MemoryStream stmMemory = new MemoryStream())
                        {

                           int count = 0;
                            do
                            {
                                count = responseStream.Read(buffer, 0, buffer.Length);
                                stmMemory.Write(buffer, 0, count);

                            } while (count != 0);
                            
                            arrayByte = stmMemory.ToArray();

                            HttpContext.Current.Response.AppendHeader("Content-Length", arrayByte.Length.ToString());
                            HttpContext.Current.Response.BinaryWrite(arrayByte);

                            HttpContext.Current.Response.Flush();
                            HttpContext.Current.ApplicationInstance.CompleteRequest();
                        }



                    }
                }
            }
            catch (Exception ex)
            {
                System.Diagnostics.Debug.Fail(ex.Message);
                System.Diagnostics.Debug.Fail(ex.StackTrace);

            }
        }