AIX files are designed to be consistently viewable and printable across different platforms. They are commonly used for distributing documents on the Web and are becoming a standard interchange format for content delivery. AIXs are editable in many graphics applications and can retain annotation, labeling, and attribute data for map layers. AIX exports from support embedding of fonts and thus can display symbology correctly even if the user does not have Esri fonts installed.

Reference

AIXFormat Members
ArcGIS.Desktop.Mapping Namespace