ARCHICAD can back-save project files in the previous ARCHICAD version. As example if you have an ARCHICAD 21 project, you can save it back to ARCHICAD 20 but not to ARCHICAD 19.
To back-save:
- In the Save dialog box, choose ARCHICAD xx Project from the Save as type list.
Before back-saving a project, always check the Migration Guide: