Word contains functionality to merge documents that evolved from a same
source. To do so, on each edit session, special identifiers are added to the
document indicating where something new was added or something old was
removed.
If the only thing you did in the last edit session is add new data, then
those identifiers could be used to remove the data. If data was removed,
then the identifiers mark that data was deleted at a certain point but not
what that data was.
Note that undoing those things isn't really straightforward and you would
have to delve into the raw xml.
Yves
