Everything opens one. That is the whole point of it, and the reason it is still around.
Convert an .rtf file to Markdown
Rich Text Format is plain text with instructions in it: `{\rtf1` at the start, then control words like `\b` for bold and `\par` for a new paragraph, all the way down. Microsoft published it in 1987 and stopped developing it in 2008, which is exactly why every word processor written since reads it.
TextEdit on a Mac and WordPad on Windows both open one without installing anything, and so do Word, LibreOffice, Google Docs and Pages. On a Mac, pressing space on the file in Finder shows it.
It is also readable as it stands: open it in a text editor and the words are there between the control words, which is more than can be said for a `.docx`.
Because it is what a Mac produces when text leaves an application. Drag a selection out of one window and into another and macOS hands over RTF; the same is true of a great deal of copy and paste between programs, and of anything exported by an older system that wanted to keep bold and italic without committing to a format.
It carries almost no metadata and no macros, which is also why it turns up as the safe option for sending a document to somebody outside an organisation.
Bold, italic, strikethrough, links, lists and tables all convert. Headings are the one thing the format is vague about: Word writes an outline level and means it, and a Mac writes nothing but a larger bold line — so the outline level is used where there is one, and a bold paragraph set larger than the body is read as a heading where there is not.