Can you help me to add a line at the very bottom of each invoice that mentions my name trading as etc please?

Hello Info-sustainable, 

Welcome to the Community page, 

In your quickbooks account, if you click on the cog wheel right hand side at the top> then select custom form styles under settings  > select the template and you can enter all the information you want to show on the invoice in there in the different sections of that page then save it. Once you then create an invoice for a customer if you click on more then print or preview it will then show all the information entered on the invoice there so you can see it before sending it off to your customer.