You can export Outlines using the File menu on macOS and by using the context menu in the Documents view on all platforms.

PDF Doc

This exports a PDF file by treating the Outline as a document. See The Notes Field.

PDF List

This exports a PDF file as a traditional outilne.

Markdown Doc

This exports a Markdown file by treating the Outline as a document. See The Notes Field.

Markdown List

This exports a Markdown file as a traditional outline using Markdown’s list syntax.

OPML

This exports an OPML file as a traditional outline. It uses some extensions to the OPML spec that are common among outliners. It also uses Markdown for formatting inside text fields.