Challenge 3: Recovering an Untracked Edit History — Solution Walkthrough

How to see what the colleague actually changed:

Use Review > Compare. Select the ORIGINAL file you sent them as one
side of the comparison, and their edited/returned file (saved under
its new filename) as the other side. Word generates a brand-new
document showing every difference between the two files as proper
tracked changes — insertions, deletions, all attributable and
reviewable exactly as if Track Changes had been on the whole time.

Why simply opening their returned file and turning Track Changes on now would not work:

Turning on Track Changes at this point only affects edits made FROM
THIS MOMENT FORWARD — it has no ability to retroactively detect or
reconstruct changes that already happened before it was switched on.
The colleague's edits are already permanently baked into that file's
actual content, indistinguishable from text that was always there;
there's no hidden "before" state stored inside a single file once
changes have been made without tracking. The only way to recover what
changed is to compare that file AGAINST something else — specifically,
the original version you still have a separate copy of — which is
exactly the situation Review > Compare exists to solve.

WHY THIS WORKS AS AN ANSWER
------------------------------
This is precisely the scenario this chapter frames Compare as solving
that Track Changes alone cannot: reconstructing a genuine edit history
after the fact, from two separately-saved files, when no tracking
happened in real time. It only works because a genuinely separate,
unmodified copy of the original still exists to compare against — had
the original file been overwritten instead of saved under a new name,
even Compare would have nothing left to compare it to.