Use FILFMT to set the default file format LINGO uses when opening a new document. The options are:

The LG4 format is the default file format for Windows versions of LINGO. This is a binary format that is readable only by LINGO. This format enables you to have custom formatting and fonts in your models, and allows you to use LINGO as an OLE server and container. Files written in LG4 format are useful only on Windows hardware.

The LNG and LTX formats are text based.  Given this, LNG and LTX files may be read into other applications.  However, these formats don’t support custom formatting and embedded objects.  In general, LNG files use LINGO syntax, while LTX files use LINDO syntax.