As a manager / an admin, I can be assured that any download call in the UI triggers a download event. Currently, the default viewer provides a download option and a print option that are transparent to the server.
The download button and the print buttons are removed from PDF.js. Reason is many customers want a specific download permission, and these buttons bypass it.
When using the PDF.js viewer (default viewer) download or print button, a download audit event is sent to the server and it is stored as a "Download".