ApprovalMax allows Quotes Requesters to copy accepted Quotes to Invoices.
Please note: the Quote Requester needs to be added also as a Sales Invoice Requester in the "Sales Invoice" workflow.
This is how it works:
Open an accepted Quote, click on "COPY TO" and select the option "Copy to Sales Invoice":
The Quote will now be copied to the Sales Invoice, with a note for the Approvers included.