.MXT File Extension
What is an MXT file?
Geographical map template created by ArcMap, a GIS mapping application included with ESRI ArcGIS Desktop; stores the base properties of a map as well as the layout positions and visibility of application toolbars; enables users to create multiple maps from the same starting point.
ArcMap uses a file named Normal.mxt as the default template for every new map created in the software. The file is located in \Documents and Settings\[user]\Application Data\ESRI\Templates\ and can be modified to create a custom default template.
If no user-specific Normal.mxt exists in the user's templates directory, ArcMap then searches for the file in the ArcGIS\Bin\Templates\ installation directory and copies it to the user's templates directory.