.AVX File

File extension avx is traditionally used for one of the default file type in ArcView, a geographic software for Microsoft Windows developed by Esri.

This type of .avx files is used for Extension Plugins which are used to add new features or support to ESRI software.

Files with suffix suffix can be typically encountered as plugins for ESRI ArcView GIS program. These can be added to the program to import more functionalities. 

How to open:

You can add and import these files to ArcView and perhaps other ESRI programs.

How to convert:

A conversion of any kind for plugins is generally highly unlikely.