Q:  For email campaigns, I would like to attach a pdf file to email to send to all invitee or attendees, how do I do that? 

A: There are 2 options:

1. If you send from Invitee or Attendee Grid, you can click on Attach file:

2. If you send from Campaign, you can Attach the file through the feature "Attachment" 

You can attach multiple files as well, but total attachment size should be less than 10MB.