Autosaved backup file created by ArchiCAD, a BIM (Building Information Modeling) program used for the designing and construction of buildings; saves a backup copy of the current project (.PLN file); automatically created by the software if the backup option is set in the application's Data Safety Preferences.

BPN files are created at regular intervals based on the user-specified application preferences. The backup is saved to the same directory as the PLN project file. If the project file becomes corrupted, you can rename the ".bpn" extension to ".pln" and use the backup as your main project file.