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

CDA -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 -based documents open within the CDA Viewer.