I've found this is super hard to explain to people who haven't had to deal with it. I have, in sending fiction stories back and forth to editors. The formatting for those is ridiculously simple... except that you need absolute 100% compatibility with Word's document revision tracking features to see your editor's comments, respond to them, accept or reject their changes, and so on. And while I haven't checked in a couple years, when I did, the only non-Microsoft stuff I found that could do it reliably were two commercial, Mac-only word processors (Apple Pages and Nisus Writer Pro). I hadn't heard of OnlyOffice before this; if I ever switch to Linux, I'll keep it in mind.