The only other way is if you have the programs for all the versions between 12 & 18.
Save 18 file as version 17.
Open in 17 and save as 16.
Open In 16 and save as 15.
Keep going till you get to 12.
You can only save back one version at a time and you may lose information relating to new features.
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