You can include links. We don't support attachments, but if you put the documents in a publicly accessible place on the internet you can link to them.
On the Promote page, there are "Edit Student Welcome Email" and "Edit Volunteer Welcome Email" buttons. Click the appropriate button to edit the message that appears in the email and the "Thank You" page following registration. If you put full links (including the http:// or https://) in your message they will appear as clickable links.
Customer support service by UserEcho