Overview
A pro-forma is a document sent by a supplier to a buyer to tell them the estimated price of the goods and services they want to buy. It’s more formal than a quote, but not as formal or final as a true invoice. Pro-forma documents are purely informational and non-binding.
A pro forma order generates a document that can be shared with a supplier before a Purchase order (PO) is confirmed.

Purpose
A pro forma order creates a report that you can share with the vendor prior to an order being confirmed. It doesn’t create any journal information and will be useful in cases where the order details are subject to change. For example, you might have to send a purchase inquiry to the vendor to inquire about prices, discounts, or delivery dates.
In Dynamics 365
In Dynamics 365 Finance & Supply Chain Management, POs that have an approval status of Approved can go through additional steps before they’re confirmed.
A pro forma confirmation document can be generated on a purchase order via the Purchase tab in the action pane.
