adoc

adoc is the file extension most commonly associated with AsciiDoc, a plain-text markup language designed for lightweight authoring of technical documentation. Documents saved with .adoc or .asciidoc are written in a human-readable source format and can be converted to richly formatted output such as HTML, PDF, EPUB, or DocBook. The adoc ecosystem centers on the AsciiDoc language, with the Asciidoctor project being the most widely used processor for rendering adoc sources.

AsciiDoc (and adoc files) support a structured approach to documentation. Authors use simple markup to define sections and subsections, lists, tables, and images, as well as cross-references, footnotes, and citations. The language also provides features for reusing content through attributes, variables, and include directives, enabling consistent formatting and easier maintenance across large collections of documents. Conditional content allows output to vary by target format or user-defined conditions.

The adoc format is popular in software development and technical documentation due to its readability in source form and its ability to produce multiple deliverables from a single source. It is commonly used in open-source projects, developer portals, and internal documentation workflows. While AsciiDoc has several implementations—most notably Asciidoctor—it remains a portable, processor-agnostic approach to lightweight markup, with adoc serving as both the file extension and a shorthand reference to the AsciiDoc ecosystem.