A commercial invoice is the most common part of your shipping documentation, and is required for most shipments. It should have the shipper’s information and logo, the invoice information, the consignee’s information including tax ID or VAT number, if required, as well as a phone number. It will have each item listed in the shipment with a corresponding HTS code and value for customs.
Pro forma, in Latin, means as a matter of form, and applies to practices or documents that are done purely as a formality. This type of invoice is merely a listing of goods, along with much of the other information required by standard commercial invoice, and it’s a signal to a customs official that the items in the shipment are not for resale. Examples of items that might be shipped using a pro forma invoice include: samples, personal effects, trade show equipment and materials, marketing materials, or items for repair or replacement and return.
You’ll never have a situation where both are used, it’s an either/or situation.