At the time of this writing, there is no defined and publicly available definition of the default formatting of the output of exporting a page to PDF.

As a result, as time progresses, there can be subtle differences in the output of existing pages which can disrupt certain processes involving sharing Confluence page content by way of PDF.

For example, the size of the text given the same font size can and has changed over time.

In order to ensure proper setting of expectations, as well as to ensure that changes in functionality do not unintentionally modify the formatting of end-user PDF exports using default settings does not result in potentially breaking changes.