Attaching Invoices To Custom Emails

Firstly, the plugin is a life saver. Thank you.

The question I have is, we are using PDF Invoices & Packing Slips for WooCommerce from WP Overnight and I would like to automatically attach the invoice to the extra emails. We send emails to our stores depending on where the customer chooses to pickup their goods at.

I am able to direct the emails to the correct stores, but when the item details are shown, they are missing the SKU numbers from the email. Our folks at each store need the sku to be able to pick the correct items.

So, how do I attached the invoice for each order?

Thank you!