Scenario
User wants to print the customer account number / entity ID in the advanced PDF/HTML template.
For example user would like to print Customer entity ID on Sales Order printouts.
Solution
Use the tag: ${record.entity.entityid}
This is usually used by customers who have smaller headers within their advanced PDF/HTML templates and the full company name would be too long for it.
The sourced information depends on the setup of your account > if you use Auto-Generated Numbers or not.