var fileInfo = new FileInfo(fileFullName);
string fileName = Path.GetFileName(fileFullName);
HttpContext.Current.Response.Clear();
HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment; filename=" + fileName);
HttpContext.Current.Response.AddHeader("Content-Length", fileInfo.Length.ToString());
HttpContext.Current.Response.ContentType = "application/octet-stream";
HttpContext.Current.Response.Flush();
HttpContext.Current.Response.WriteFile(fileFullName);
HttpContext.Current.Response.End();
}
this code will download any file