Invoice format refers to the layout of an invoice and the different sections it includes. Invoices can be broken down into different sections which allow you to arrange the information in a logical way, whilst making sure you include all the necessary information that is required to be stated on an invoice.
Invoice format is not the same as invoice template. A template is an already formatted invoice with dummy data that you can replace with your own information. Accounting softwares such as Xero or Quickbooks allow you to generate invoices using their pre-made templates but also give you the ability to amend the format. Using these templates and editing elements of it, such as text, font sizes or your logo is the standard approach to customising your invoice. However, it doesn't offer as much creative freedom as branding your invoice does, which is what can be achieved by creating a custom DOCX branding theme for your business.