If you are a student, Graphisoft provides free educational versions. While they focus on the newest releases, you can sometimes request older installers through their support portal.
ArchiCAD 16 relied heavily on WibuKey or CodeMeter hardware keys. Most torrented versions try to "emulate" this key. If the emulation fails, the software will only run in "Demo Mode," which prevents you from saving your work. Technical Tips for Installation torrent archicad 16 64 bit work
Right-click the .exe and set it to Windows 7 compatibility. If you are a student, Graphisoft provides free