WooCommerce PDF Invoices and Packing Slips Pro (Challan Pro) will help you attach a PDF invoice to your order confirmation email.

Foxtrot is a customer, invoice and expensemanagementsystem designed for small businesses and freelancers.

WooPrintInvoice - Order Invoice Printing for WooCommerce is a WooCommerce add-on for print order invoices, form the admin and customer side.