[chralieboy]

The "micro" in "microservices" refers more to the size of their conceptual complexity than how large of a task it actually is.

PDFs are one conceptual bucket that can have their own datastore and a simple API. Sending email isn't included in that service's contract, as it actually outsources this task to Mailgun.

REST/JSON can have formal specification – check out http://json-schema.org/. Swagger (http://swagger.io/) is another example of this and works really well for automatically generating client libraries in many languages and auto-updating documentation.