In an ASP.NET framework, HttpHandler is used to handle the specific request based on file extensions.
It is a special type of class that implements the System.Web.IHttpHandler interface. And When IHttpHandler receive the request from the web browser, it checks the extension of the file and handles the request Or perform some operation based on that requests. Generally, it is an extension based processor that is responsible for fulfilling the request from a browser and also based on their file extension.
Request Response

Here we describe the few HttpHandler and their file extension-

Example-
namespace CustomHttpHandler
{
public class MyHttpHandler : IHttpHandler
{
public bool IsHandler
{
get { return false; }
}
public void ProcessRequest(HttpContext context)
{
throw new NotImplementedException();
}
}
}