Document Reference
The DocumentReference resource is used to reference a clinical document for a patient within the health system. This resource supports reading Continuity of Care Documents (CCD), returning a list of clinical documents, and a reference to retrieve a document as a PDF.
Document Reference API returns different type of document e.g. Assessment note, Consult note, Discharge Summary, Ultrasound Report, etc, Attachment (the document or URL of the document), date (when the document was created), Author (who created the document), Custodian (organization/group responsible for ongoing maintenance of the document).
Based on:
http://hl7.org/fhir/us/core/StructureDefinition/us-core-documentreference