To save scene data
in a non-native file format such as OBJ or DXF, you must have a
plug-in for that file format loaded.
The mayaAscii and
mayaBinary file formats are the only ones that preserve all the
information contained within your scene. Setting the output format for
an export using the Export Options
box will change
your default export format for the current and subsequent export
operations. If you set the output format to something other then
mayaAscii or mayaBinary and export using that format and then quit
without saving the entire file then you can lose data.
Always check the export
type in the export file browser to ensure you are writing the file
using the expected file format.