MS AJAX UpdatePanel throws Sys.WebForms.PageRequestManagerParserErrorException at 11:02 AM

I wrote ASP.NET code to call a service to generate and download a PDF file. At first, I tried to use AJAX UpdatePanel in the ASP.NET code to show progress because the service call may take long time. When the service call returned, I wanted to show the PDF file directly in browser on the same ASP.NET page:

  // Stream PDF kit to client
  Byte[] buffer = File.ReadAllBytes(filePath);
  base.Response.Clear();
  base.Response.ContentType = "application/pdf";
  int length = buffer.Length;
  base.Response.AddHeader("Accept-Header", length.ToString());
  base.Response.AddHeader("Content-Length", length.ToString());
  base.Response.OutputStream.Write(buffer, 0, buffer.Length);
  base.Response.Flush();
  base.Response.End();

But I saw this exception message:

Sys.WebForms.PageRequestManagerParserErrorException: The message received from the server could not be parsed ...

Then I realized the UpdatePanel JavaScript tried to parse the returned data for the original web page, but it received strange PDF stream instead. I found the explanation here:

The UpdatePanel control uses asynchronous postbacks to control which parts of the page get rendered. It does this using a whole bunch of JavaScript on the client and a whole bunch of C# on the server. Asynchronous postbacks are exactly the same as regular postbacks except for one important thing: the rendering. Asynchronous postbacks go through the same life cycles events as regular pages (this is a question I get asked often). Only at the render phase do things get different. We capture the rendering of only the UpdatePanels that we care about and send it down to the client using a special format. In addition, we send out some other pieces of information, such as the page title, hidden form values, the form action URL, and lists of scripts.

It turned out that I should using Response.Redirect() to another page to show the PDF file in browser. To avoid the same exception, there is no AJAX code in the second page.