How old is the file?
Any Archicad version since version 10 can open files back to version 10.
To open files older than that you can download a file converter from here.
https://graphisoft.com/downloads/fileconverter
Or is the problem that you don't have Archicad?
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11