ADOC, AsciiDoc File (.adoc)
The ADOC Document file format
ADOC files are simple text documents that contain plain text only. They can include special syntax markers, including periods, colons, square brackets, and others. These special characters allow the content of the file to be displayed using custom formatting. Text processing software such as Asciidoctor can export ADOC files in another format as well, such as HTML or EPUB.
Technical details of ADOC files
The most common usage case for ADOC files is in software documentations. They can be used for a variety of purposes though, that requires a plain text document. Especially on GitHub, you can find many program documentations saved in the AsciiDoc format. Technically, ADOC files are not that different from TXT files. They use the .adoc file extension to indicate, that the syntax used in the file is according to AsciiDoc.