What is the MD file format?
A file with the .md extension contains a plain text document created using Markdown language. Many dialects of Markdown exist, but all use the same set of conventions and similar syntax. Markdown tags define text formatting elements such as:
- Bold and italic attributes
- Headers
- Table format
- Lists
- Block quotes
- Image and HTML code embedding
.md files can also use the .MARKDOWN suffix. .md files can be easily converted to an RTF or PDF format, although initially Markdown was primarily used to generate HTML documents, typically help files. Since .md is a plain text file, it can be opened and edited with any text editor to create formatted documents. Markdown uses a simple and easy-to-read syntax.
Markdown was developed in 2004 by John Gruber, with contributions from Aaron Swartz. The main goal of the designers of this language was to offer users a simple and intuitive markup system - unlike HTML, for example - for editing and creating documents. The original .md file interpreter, which converted .md files into HTML documents, was written in Perl. Many variations of the Markdown language have been developed since then. In 2016, RFC 7763 registered the text/markdown MIME type, and RFC 7764 catalogued the major Markdown variants, including CommonMark, GFM, Markdown Extra, and others.
Security & safety
RISK: LOWA .md file is plain text and cannot execute code, so opening one is safe. The only caveat: Markdown allows raw HTML, so a rendered preview could contain HTML/JavaScript or images that phone home - reputable renderers (GitHub, VS Code) sanitize this. As always, distrust links inside a document from an unknown source before clicking.
Format details
in a nutshellFULL NAMEMarkdown Document
DEVELOPERJohn Gruber (with Aaron Swartz), 2004since 2004 (Markdown by John Gruber); CommonMark spec 2014; GitHub Flavored Markdown 2017
CATEGORYDeveloper Files
MIME TYPEtext/markdown
TYPEplain-text markup (lightweight markup language)
STANDARDOpen · royalty-free
Programs that open MD files
Windows5 apps
Windows Notepad
Built-in Opens the raw Markdown text for quick reading/editing - no formatting preview. 
Notepad
Open-source Open for editing with syntax highlighting; install the MarkdownViewer++ plugin for preview. 
macOS3 apps
Linux3 apps
Vim / Neovim
Open-source Edit with syntax highlighting; preview via plugins (e.g. markdown-preview.nvim). 
Technical details
deep spec| MIME type | text/markdown (registered by RFC 7763, 2016) |
| Character encoding | UTF-8 plain text; no binary header or magic bytes - identified by the .md extension and conventional syntax |
| Syntax style | Lightweight markup - source is human-readable without a parser or renderer |
| Primary output target | HTML, produced by a Markdown processor; secondary targets include PDF and EPUB via tools such as Pandoc |
| Common dialects | CommonMark, GitHub Flavored Markdown (GFM), Markdown Extra, MultiMarkdown, R Markdown (.Rmd) |
| Front matter support | YAML front matter between --- fences is widely used by static-site generators (Jekyll, Hugo, Eleventy) to store page metadata |
| Heading syntax | ATX style (# H1, ## H2) and Setext style (underline with = or -) are both valid in the base spec |
| Link syntax | Inline [text](url), reference-style [text][id], and autolink <url> - all three forms are part of the core spec |
| Code block syntax | Fenced (triple backticks or tildes) or indented 4 spaces; a language identifier after the opening fence enables syntax highlighting |
| Table support | Not present in the original 2004 spec; introduced as a GFM extension and later as a CommonMark optional extension |
| Image syntax |  - stores only a URL reference; images are not embedded in the .md file itself |
| Strikethrough | ~~text~~ - a GFM extension; absent from the base Markdown spec |
| Math / LaTeX support | $inline$ and $$block$$ syntax recognized by Obsidian, Jupyter, and VS Code extensions but outside the core spec |
| Line-break rules | A blank line separates block elements; hard line breaks require two trailing spaces or a \ before a newline (CommonMark) |
| Extension conflicts | .md is occasionally claimed by metadata or machine-description tools; file content and context distinguish Markdown use |
| Released | 2004 (Markdown by John Gruber); CommonMark spec 2014; GitHub Flavored Markdown 2017 |
| Open standard | Yes · royalty-free |
| Specification | spec.commonmark.org |
MD conversions
Possible
.MD .PDFGUIDE
Yes - the fastest method depends on your setup: Typora or Obsidian users can export via File > Export > PDF…
How to convert
.MD .HTMLOnline converter
Yes -- Markdown was designed to produce HTML, and Pandoc converts it in one command: pandoc file.md -o…
How to convert
.MD .DOCXOnline converter
Yes -- Pandoc converts MD to DOCX in one command and is free on all platforms.
How to convert
.MD .TXTOnline converter
Yes -- a Markdown file is already plain text, so a rename is enough; or strip the syntax marks in any text…
How to convert
.MD .EPUBOnline converter
Yes - Pandoc converts a Markdown file to EPUB with a single command.
How to convert
Community Q&A
asked by users
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Frequently asked questions
How do I open an MD file?
Any text editor opens the raw text. To see it formatted, use VS Code (Ctrl+Shift+V preview), Obsidian or Typora, or view it on GitHub, which renders Markdown automatically.
What is a README.md file?
It's the front-page documentation of a code project, written in Markdown. GitHub, GitLab and Bitbucket render it automatically on the repository home page.
How do I convert Markdown to PDF?
Use Pandoc (pandoc file.md -o file.pdf) or an editor's export: Typora, Obsidian and the VS Code Markdown PDF extension all export directly to PDF.
Is MD the same as a text file?
Yes - Markdown is plain text with formatting conventions. You can rename .md to .txt and it still opens; the .md extension just signals it should be rendered as Markdown.
What's the difference between Markdown and GitHub Flavored Markdown?
GitHub Flavored Markdown (GFM) extends the CommonMark standard with tables, task lists (- [ ]), strikethrough and auto-linking - the variant you see on GitHub.
Can I open an MD file on my phone?
Yes - Obsidian and many text/Markdown apps exist for iOS and Android, and viewing the file on GitHub in a mobile browser renders it too.
References
1CommonMark - Markdown specificationspec.commonmark.org
2GitHub - Basic writing and formatting syntaxdocs.github.com
