When installed the module adds a file upload option into the order details in your backend. An employee can then upload multiple files. You can also set a file as a default invoice, when the customer downloads the invoice this file is used instead of the default invoice generated by Prestashop.

This is especially useful when the default invoice does not meet your country's regulations, or if you need to use an external system to generate these invoices. You could upload a scanned copy of your own invoices or use a file generated by any other system.