Microsoft filed a covenant not to sue and made all the formats open ~20 years ago. A lot of people bitched at the time but there's a long list of software that supports the format now. It is complicated because the apps themselves are complicated and decades old, and imperfect because the format or app you're converting to likely doesn't support all of the features and certainly none of the quirks.

https://en.wikipedia.org/wiki/Office_Open_XML

It took browsers 15 years just to render HTML whitespace nearly consistently, so keep that in mind as you read that history.