Interoperability through document-based meaningful exchange of Personal Health Records and Electronic Health Records has to be supported by portable document formats. For HL7 structured documents, XML offers an encoding syntax which guarantees interoperability. However, portability is not guaranteed when other files and related documents have to be attached to the structured documents, as it might be necessary to know in advance (or modify) the location (path) of the referenced objects. The objective of the paper is to propose a standard file format for electronic health documents which improves their portability, human readability, and usability. The proposed DUFF HL7 specification complements the HL7 v3 structured document standards, encapsulating the content and information attached to the electronic health documents in a single file.