They can be found in present-day transactions, although they are less common today.
In either case, the receipt was important, as it stood as your proof of delivery.
Most billheads would bear the company's name and address, a unique invoice number, the payment terms, line items for products or services, a total, and (optionally) handwritten notes.
Billheads are considered to be vintage ephemera.
In some cases, a relative or ancestor may have owned the business or even have signed the document.