Hello,
When it comes to Document Templates (Quotes/Invoices) & Forms, there are a difference between them. While it is possible to have a Form output include the Invoice content, it is not treated as one (an Invoice for example) within ServiceM8. What this means is, there will be parts of your workflow which will be broken or at best disjointed from the Customer's perspective. The best area to illustrate this would be if you have a Form which outputs the Form's content and the Invoice content; when you email the customer and include the Form "Invoice", you will have to decide if you want the customer's attachment in the email to differ from the Invoice document they would see in the pay link.
This is not to say it can't or shouldn't be done, and we have clients who use Forms like this in their ServiceM8 workflow and they have adjusted their utilization of ServiceM8 to accommodate this.
I would ask and recommend that we set up a call to review your specific workflow needs more closely, and find the best way to execute a solution and workflow that works for your team's needs:
https://dddesigned.page.link/quickcall