What are .ashx files in an ASP.NET application?

In short, a file ASHX is an ASPX file, minus all plumbing ASP.NET webform.

I am using ASHX to generate PDF files on the fly, and download them. Similarly, I use them to generate thumbnails on the fly and download them.

This could work very well with a blank ASPX, but ASHX files are much less resource-consuming.

Take a look at this tutorial to see how the files ashx.