.ATC File Extension
File TypeAutoCAD Tool Catalog File
What is an ATC file?
Tool catalog file used by the AutoCAD design and documentation CAD software; contains definitions for all of the tools in a user interface palette; used for storing tool configurations and customizing the AutoCAD workspace.
AutoCAD creates an ATC file whenever the user defines a new palette on the interface.
NOTE: You can export a palette stored in an ATC file using an .XTP file.