Why a file won't open

Unmarked reads text. It declines a file when it isn't text: a binary file, a file over 25 MB, or one in an encoding it can't read safely. That's a deliberate call. Unmarked autosaves as you type, and it would rather not open a file than risk writing garbage back over your work.

A .md file is plain text under the hood. So is .txt, .markdown, and the rest. When one won't open, it's almost always one of three things.

It's a binary file, not text

A file with a Markdown-looking name can still be binary inside. A PDF saved as notes.md, an image, a Word .docx, a database file. Unmarked checks the contents, not just the extension, and stops when the bytes aren't text.

Open it in the app that made it instead. If you want a Markdown copy, export from that app, or paste the text into a new Unmarked document.

It's over 25 MB

Unmarked caps files at 25 MB. A plain Markdown file almost never gets that big on its own; when one does, it's usually a log dump, exported data, or a document with large content pasted in. The cap keeps the app responsive and keeps autosave safe on files that size.

If you have a genuine text file above the limit, split it, or tell us what you're working with and we'll take a look.

Unmarked can't read the encoding safely

Unmarked handles the encodings real files come in: UTF-8, UTF-16, UTF-32, Windows-1252, and Latin-1. A file from Windows Notepad opens and saves back unchanged. But if a file is in something it can't identify with confidence, it declines rather than guess. Guessing wrong would mangle accents, symbols, and non-Latin text on the next autosave.

Re-saving the file as UTF-8 in the app that created it usually fixes this.

When Unmarked declines a file, nothing is lost. It hasn't touched it. The whole point of declining is to avoid writing back over a file it can't read cleanly, so there's no half-opened state and no autosave to undo. Your file is exactly as it was.

A .md file opens in a different app instead

This one isn't Unmarked declining the file. If your .md file opens in TextEdit, Xcode, or some other editor on a double-click, that's the macOS default-app setting, not Unmarked. Fix it once in Finder. See Make Unmarked your default Markdown app.