Set future "Pay not later than [date]" on invoice

There is a way to use WooCommerce PDF Invoices just as an invoice and not only as a receipt on an already paid transaction. If selecting “Cash on Delivery” in WooCommerce check-out, an invoice will be produced, that can be paid by customer before receiving the product or service.

However, (and here is my request) there is no way to insert a particular future due date on to the PDF invoice from admin page (e.g. Insert Due Date: [today] + [14]). It would be great to set a date e.g. two weeks forward in time, counting from date of registration/purchase in WooCommerce so there would be a note “Pay invoice within due date 2015-12-19” printed on the PDF.

https://www.ads-software.com/plugins/woocommerce-pdf-invoices/