LibreOffice

LibreOffice is the default answer to "what replaces Microsoft Office". On most beginner distributions it is already there when you first log in, and it opens the Word, Excel and PowerPoint files you brought across from Windows.

Coming from Office, the first hour feels like stepping back a version or two. The commands are nearly all present but they sit in menus rather than the ribbon, so you spend a little while hunting. Basic letters, budgets and slide decks behave exactly as you expect. Where it bites is at the edges: a heavily formatted CV or a spreadsheet full of Excel macros can come out wrong, and there is no live shared editing.

If your documents mostly stay on your own computer, this covers the job at no cost. If you are sending tightly formatted files back and forth with an office that runs Microsoft 365 every day, expect some tidying up, and keep the free Office web apps in a browser tab as a backstop.