1. Activate Form Workflow Plus Add-On
2. Start G Merge Plus: Mail & Doc Merge with Attachments => Link to install
3. Set up G Merge Plus (See also: A step-by-step guide to getting started with G Merge Plus)
4. In the Settings crank wheel menu of G Merge Plus add a filter selecting your Criteria header column Equal to Approved
5. GENERATE your merges Now or set it to run automatically Every hour or Daily.
NEVER choose On form submit to generate your merges this way. Form Workflow Plus must complete a process before G Merge Plus can run your mail/doc merge.