You can select the email notifications in which you want to attach the document in WooCommerce > PDF Invoices > Documents > Invoice > Attach to setting:
The set-up displayed in the above screenshot would make the PDF invoice attachment/creation trigger only when the order reaches the “Completed” status.
Please note that attaching the document will create a new invoice for the order, consuming an invoice number. Therefore, if you select “New order”, the document will be created as soon as the order is placed, generating a new invoice number.
