vTiger - custom action button in detail view for module

I have a custom module called "Billing" which is used to send invoices for telco services to clients (separate from the standard Invoice module). I want a button at the top of the detail view that re-sends the invoice to the client by email on demand. The information the email would contain is from the following fields: To email address: related account field 'cf_979' From address: support@[login to view URL] Subject: 'NLB Billing - A copy of your invoice - $cf_993' Client name: 'relatedto' (accounts module) Invoice Number: 'cf_993' Issued Date: 'issue_date' Due Date: 'due_date' Amount due: 'cf_997 Attachment: file in field 'generated_pdf' (located in /var/www/html/PDF/) It would also be OK if this was to be an option in the "More" dropdown in the detail view.