You can put any file type into your /content directories, but Hugo uses the markup front matter value if set or the file extension (see Markup identifiers in the table below) to determine if the markup needs to be processed, e.g.:
To be treated as a content file, with layout, shortcodes etc., it must have front matter. If not, it will be copied as-is.
The markup identifier is fetched from either the markup variable in front matter or from the file extension. For markup-related configuration, see Configure Markup.
Some of the formats in the table above need external helpers installed on your PC. For example, for AsciiDoc files,
Hugo will try to call the asciidoctor command. This means that you will have to install the associated
tool on your machine to be able to use these formats.
Hugo passes reasonable default arguments to these external helpers by default:
The Asciidoctor community offers a wide set of tools for the AsciiDoc format that can be installed additionally to Hugo.
See the Asciidoctor docs for installation instructions. Make sure that also all
optional extensions like asciidoctor-diagram or asciidoctor-html5s are installed if required.
Some Asciidoctor parameters can be customized in Hugo. See details.
Markdown syntax is simple enough to learn in a single sitting. The following are excellent resources to get you up and running: