If you want a printout of the invoice as an attachment to the invoice, you can print one through the service request/or maintenance note process.
Example of printing an invoice attachment from a service request
Go through the process menu Service requests > Manage requests
Search for completed cases through Search. Open the case from which you want to print an invoice attachment.
In the extended view of the case, click Advanced functions, and then click Request report
The case report opens on another tab.