Magento 2 Invoice PDF Generator - helps you to customize the pdf templates for Magento 2. If you have an enabled template and a default template for the store you need your template the system will print the pdf template. For the moment there is not a system configuration switch but it will be added as soon as we finish with the permissions and the api interfaces.
For the variable system you can read the Magento domentation here: http://devdocs.magento.com/guides/v2.0/frontend-dev-guide/templates/template-email.html. We use the exact same system to generate the variables.