An aspx file with the ASPX file extension is an Active Server Page Extended file that is specially designed for Microsoft's ASP.NET framework. They are also known as .NET Web forms. ASPX files are not the same as the Web Handler files ASHX although they look similar.

ASPX files are generated by a web server which contain scripts and source codes that help us to communicate to a browser and tells how a web page should be opened and displayed.

More often than not, we will probably only see the extension .ASPX in a URL or when our web browser accidentally sends us an ASPX file instead of the one we thought we were downloading.