Most businesses use the same sorts of information on invoices: contact information, sequential invoice numbers, etc. Because of the unique nature of freelance work compared to other businesses, especially for freelance invoices, it should be adapted to reflect these differences.
A pro forma invoice describes the value of a transaction prior to its completion. The term pro forma refers to a planned business transaction. Pro forma invoices are commonly used when two companies are just starting to do business together and for international trade. The invoice describes the terms of a deal and can sometimes be used to expedite the customs and shipping processes.
Some other sample invoice where all you need to enter is a description of work and amount billed. You have to manually add lines and tax to calculate total. Marketing banner in the footer of this invoice allows you to advertise other services your company provides.
Back in the days before e-commerce, every job was billed using paper invoices, everyone was paid with paper checks, and all those paper records were delivered in person or sent in the mail. Back then it was easy to put together the information needed for an invoice. For the self-employed freelancer in the 21st century, things are no longer that simple and it affects what you put on your personalized invoices.