A GDC file contains compiled GDScript source code, which is a scripting language used to create and modify content in Godot Engine. It stores bytecode compiled from a .GD source code file, which improves the performance of the 2D or 3D game developed in Godot Engine. GDC files are typically packaged with .ZIP or .PCK Godot Engine Game Pack files when a user deploys a game.

Godot Engine is an open source game engine used to create 2D and 3D games for various platforms, such as Windows, macOS, Linux, Android, iOS, and the web. GDScript was created by the Godot community to provide custom integrated features for developing games. GDC files are most often created when a user exports the resources of a project by selecting Project → Export, and then click Export PCK/Zip. Once the GDScript is compiled into bytecode it cannot be opened or opened or edited by Godot Engine. The file is meant to be referenced by the game it is packaged with. NOTE: GDScript was introduced with version 3.1 and later of Godot Engine.