In the mid 1970s, when a group at the Brigham Young University Law School set out to create a software application that would automate the production of rule-based legal documentation, the group coined the phrase Document Assembly, a term descriptive of the process of using the software application (commonly referred to as a template) to generate a custom document.
Some years later, the term Document Automation came into popular use, and while many consider the term to be synonymous with Document Assembly, it differs in that it actually describes the template development process—building scripting logic (or business rules) into the text of a document, in fact, transforming the document into a template. Put another way, Document Automation describes the process of engineering templates, while Document Assembly describes the process of using the templates to generate custom documents.
Document Generation is one of the most recent terms applied to the discipline and can be broadly used to refer to both parts of the process—transforming documents into templates and then using the templates to generate custom documents.
With that said, the reality is that most people involved in the discipline may use any of the terms interchangeably.