This must have been intended as hyperbole. It is true, in some legal practice areas, non-use of Word has been highly impractical or even impossible for a long time, mainly because in the mainstream legal profession generally Word quickly established a chokehold by the late 1990s.

Some courts expect Word format. I haven't been close to litigation in ages so I don't know how common a thing this is, but here's an example of an apparent "Word only" federal court: https://www.caed.uscourts.gov/caednew/index.cfm/attorney-inf... . So sure, in a hypothetical where a lawyer stubbornly refused to use Word in the context of a filing in that court, you can imagine consequences arising to the level of malpractice, but I don't think that's what they had in mind.

A more familiar issue to me (and I'm guessing what that speaker was thinking of) is that if you're negotiating an agreement with some other party, and they are using Word (as they most likely will be), it is going to be highly inconvenient at best to insist on using some alternative tool.

Red Hat's in house legal team is, er, was not a law firm of course, but ages ago Red Hat attempted to have as many 'back-office' staff use RHEL as possible, with few exceptions related to what was necessary for regulatory purposes. This extended to Red Hat's legal team, which attempted valiantly for a while to use OpenOffice (as was, and I suppose more specifically the RHEL packaging of the go-oo fork in those days) for all document-related purposes, including negotiating agreements with outside parties who were using Word. This proved to be impractical for at least the subset of the legal team that did that sort of work as their daily bread and butter, and eventually they got access to Word on Windows on VMware. Later on, it became possible for Red Hat lawyers to use OS X and Windows with Word, so the issue went away.