File with .OPJ extension is used to store CAD project data for PCB (printed circuit board), including project settings and references to files associated with the project, in the form of a text file. It references at least one DNS project file.

OPJ files are created with OrCAD software used for electrical circuit design. This file format serves as a common container for files asscociated with given PCB design blueprint. OPJ files can be opened and edited with any standard text editor, although this is discouraged due to risk of damaging project data.