Thank you for the clarification. This will work, but then I will need to create separate invoice templates for each customer. Is there a way to do this with a parameter - something like "[Company Name]" - so I can use one invoice template for all customers?

When I look at Reminders (the section right below Messages) I see "Use [Invoice No.] and [Company Name] as placeholders in the email." so it sounds like Invoice No and Company Name parameters are supported in certain parts of the system.