To automatically deliver PDF invoices to customers upon checkout:

1. Navigate to WooCommerce → Settings → PDF Smart Receipts → Emails.
2. Find the A4 Invoice Email Attachments multi-select box.
3. Select the email triggers you want (e.g. Completed order and Customer invoice / Order details).
4. Click Save Changes.

When WooCommerce sends those transactional emails, SemiAuto Invoicing will attach the finalized PDF invoice automatically.