The reason why these are classified as different versions, as opposed to different translations, is because there are many thousands of variations that exist between these texts. So how can scholars identify the version of the Torah that is closest to the original Torah given to Moses? Unfortunately it’s not as simple as just taking the version that has the oldest surviving manuscripts. This would be the Dead Sea Scrolls (DSS), but the problem is that the DSS are highly fragmentary and only contain small portions of the Torah. Nor can we take the version with the earliest complete manuscript tradition, which would be the Septuagint (LXX), as this contains verses that are different to the earlier DSS. The Masoretic Text (MT), which is very late in terms of manuscripts compared to the LXX, actually agrees with the DSS in some places where the LXX disagrees. Here are some examples:

In the example above, the 32nd chapter of the Book of Deuteronomy is compared between the DSS, LXX and MT. Two verses are compared, 32:8 and 32:43. Even though we are comparing the same chapter of Deuteronomy, the texts never completely agree in all verses. Sometimes the DSS agree with the MT over the LXX, as in verse 32:43 [2], and sometimes the DSS agree with the LXX over the MT, as in verse 32:8 [3].
Unfortunately no one knows with certainty which version is the closest to the original Torah given to Moses. The proof of this is the way in which scholars of the Bible construct modern translations. Every modern translation of the Bible is essentially an eclectic translation because it combines from the different versions of the Torah. Sometimes scholars go with manuscripts of the MT, sometimes the LXX and sometimes the ST. By borrowing from the different manuscripts they are essentially creating a new Torah that never existed before!