Mar 02, 2015 11:54 PM|Shawn - MSFT|LINK
HTTP modules and HTTP handlers are an integral part of the ASP.NET architecture. While a request is being processed, each request is processed by multiple HTTP modules (for example, the authentication module and the session module) and is then processed
by a single HTTP handler. After the handler has processed the request, the request flows back through the HTTP modules.
Modules are called before and after the handler executes. Modules enable developers to intercept, participate in, or modify each individual request. Handlers are used to process individual endpoint requests.
For this situation, you may refer to the following links for more information about ASP.NET HTTP Modules and HTTP Handlers :
Besides, for tracking downloads, you could also refer to the following information: