An atr file extension is related to the Autodesk Lightscape material data format.
ATR file extension - Autodesk Lightscape material data
What is atr file? How to open atr files?
File type specification:
The atr file extension is associated with the Lightscape, a visualization software for Microsoft Windows operating system, developed by Autodesk.
The atr file contains material data used by Lightscape program.
This atr file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.