title: how to download file telegram bot?
body: <p>I use bot API v15.0.0.0 and downloaded file(Photo,Document,Audio,etc.) from user with this code, but when I run, file not open and file size is 0 KB.</p>
  
  <pre><code>var message = update.Message;
  
  else if (message.Type == MessageType.Photo) {
  
    var file = bot.GetFileAsync(message.Photo.LastOrDefault().FileId);
    var fileName = file.Result.FileId + "." + file.Result.FilePath.Split('.').Last();
  
    using(var saveImageStream = File.Open(fileName, FileMode.Create)) 
    {
       bot.DownloadFileAsync(file.Result.FilePath, saveImageStream);
    }
    bot.SendTextMessageAsync(chatId, "Image save");
  }
  </code></pre>