• Nonprinting Formatting Marks by Suzanne Barnhill, MVP
• Setting Up Letter Templates - Ribbon by Suzanne Barnhill, MVP
• Automatic numbering of Word documents by Graham Mayor, MVP

They move because they are text not underlining.

Looking at your document, you are using the Enter key erratically. It is designed to end a paragraph, not a line.


Consider using Rich Text Content Controls inside table cells to type your information. Create a Form Using Word Content Controls by Greg Maxey
Create forms that users complete or print in Word - Office Support



You want your Invoice Form to be a template, not a document. The invoices will be documents created based on the template.