Arma 3 is not designed to work with previous versions' saves. This tool allows to -try- going from one version to a more recent one.
Going from a version to the next one (e.g 2.04 → 2.06) MAY be fine, two versions above quite lucky, and more than that highly unlikely. Use at your own risk, and make a backup of the previous save file.
See
Steam Branches to play with an older version of the game, compatible with the targeted save.