https://www.hl7.org/fhir/DSTU2/documentreference.html Document Reference API retrieves resource Documents by it's id. DocumentReference is used to describe a document that is made available to a healthcare system. A document is some sequence of bytes that is identifiable, establishes its own context (e.g., what subject, author, etc. can be displayed to the user), and has a defined update management. DocumentReference can be used with any document format that has a recognized mime type and that conforms to this definition. NOTE: The number of records returned is limited to a maximum of 500.