Questions How to automatically add file attachments to an outgoing email

Scenario:  Field service technician fill out reports.  Technicians time and materials are used to create invoices.  The FS reports are attached to the invoices as pdfs.

Want to automatically attach the invoice file attachments to the the email invoice to the customer.  Does anyone have a method for doing this?

Looked at the following options:

1. Using a business Event import scenario that updated the email with the attachments.  Whilst the import scenario on the Email Activity screen includes a facility to "Attach files", I can't seem to get it to work
2. Including images in the invoice.  That is a limited solution because the Report Designer does not support display of pdfs and some images may be multiple pages long
3. Including links to a website in the email, where the attachments are stored.  Possible but maybe some security issues.

Including the attachments is the preferred solution.