Some ASP.NET files are dynamic. They are generated with C# code or disk resources. These files do not require web forms. Instead, an ASHX generic handler is ideal. It can return an image from a query string, write XML, or any other data.
.ashx files are web-handler files in asp.net programming and define IHttpHandler interface. Whenever an .ashx file is requested, ProcessRequest() method is invoked automatically. ProcessRequest() is a method where we do make changes according to our requirement.
Handlers are used in URL routing, Image handling, binary data handling etc. as it support backward compatibility.
.ashx are the resource files.
.ashx file means generic handler files.it use full for retriving images,documents.
ashx is handler file which can retrive data using webservices or json
.ashx files: generic handler files
Handler Files in ASP.NET