Clinical Document Architecture (CDA Clinical Document Architecture) is an XML-based markup standard for specifying the encoding, structure and semantics of clinical documents for exchange. The CDA Clinical Document Architecture Viewer is a component within Clinical for viewing correspondence received in the CDA Clinical Document Architecture format.

CDA Clinical Document Architecture-based correspondence is viewed via the Letters tab of the patient's Clinical Window, along with other letters and documentation. Where as 'standard' letters open in the Letter Writer, CDA Clinical Document Architecture-based documents open within the CDA Clinical Document Architecture Viewer.