Convert Rich Text Format .rtf files to Markdown in your browser. RTF is plain-text markup, so the conversion is unusually clean.
RTF has been around since 1987 and it is the odd one out here: not a zip, not a binary container, just text. Formatting is expressed as backslash control words in the byte stream — \b for bold, \par for a paragraph break, \fs28 for a font size — which means the structure of the document is stated explicitly rather than implied by geometry or hidden in a style table somewhere else in an archive.
That explicitness is why RTF converts well. There is no layout to reverse-engineer the way there is in a PDF and no separate numbering part to reconcile the way there is in a .docx; the converter reads the stream in order and emits Markdown as it goes. The main wrinkle is that non-ASCII characters are written as \u escapes or as code page bytes, so an old RTF from a non-English system needs its declared character set honoured, which file2md does.
How well that works is easiest to see by comparison. Run the same document through as .rtf and as .doc — the two formats Word has offered for about as long as each other — and the RTF keeps things the binary format drops: bookmark anchors survive, so internal cross-references still jump somewhere, and the contents of a text box come through instead of disappearing. The one thing RTF gives up that a .docx keeps is image alt text, which is absent from the output rather than empty.
Images leave nothing behind — not even the alt text a .docx would keep — so a document that carries meaning in its figures loses it silently. RTF has no encryption of its own, so password protection is not a concern here.