You can associate a file with an event you created (for example, a form for an appointment or a document to share at a meeting) by attaching it directly to the event in Calendar.
Attach a file to an event: Drag the file to the event. You can also double-click or force click the event, click Attachments, then select a file to attach.
Preview an attached file: Double-click or force click the event, select the file, then press the Space bar.
Remove an attached file: Double-click or force click the event, select the file, then press the Delete key.