PDF/A-3, PDF for Long-term Preservation, Use of ISO 32000-1, With Embedded Files

Identification and description

Full name ISO 19005-3. Document management - Electronic document file format for long-term preservation - Part 3: Use of ISO 32000-1 with support for embedded files (PDF/A-3) Description

PDF/A-3 is a constrained form of Adobe PDF version 1.7 (as defined in ISO 32000-1) intended to be suitable for archiving of page-oriented documents for which PDF is already being used in practice. PDF/A-3 adds a single and highly significant feature to its predecessor PDF/A-2 (ISO 19005-2) specification, to permit the embedding within a PDF/A file a file, or files, in any other format, not just other PDF/A files (as permitted in PDF/A-2).

See PDF/A_family for more information about the PDF/A family of standards. See PDF/A-2 for information about the version of the PDF/A standard that PDF/A-3 extends.

As in PDF/A-2, the PDF/A-3 standard defines three levels of conformance: conformance level A satisfies all requirements in the specification; level B is a lower level of conformance, satisfying requirements intended to be those minimally necessary to ensure that the rendered visual appearance of a conforming file is preservable over the long term. The specification notes that "Level B conforming files might not have sufficiently rich internal information to allow for the preservation of the document's logical structure and content text stream in natural reading order, which is provided by Level A conformance." An intermediate level of conformance, Level U conformance corresponds to Level B conformance with the additional requirement that all text in the document have Unicode equivalents.

PDF/A-3 allows for embedding of files of any type, but imposes requirements beyond those in "regular" PDF 1.7 files as defined by ISO 32000-1. Files that comply with these requirements are termed "associated" files; an explicit association must be made between each embedded files and the containing PDF or object or structure (e.g., image, page, or logical section) within the PDF. See Notes below for more detail on the association mechanism. Predefined values for relationships for associated files (in the required AFRelationship key) are Source, Data, Alternative, Supplement, and Unspecified. MIME types must be provided for associated files. The PDF/A-3 specification requires the use of application/octet-stream if a more specific MIME type is not known. The compilers of this resource have not determined whether more explicit characterization necessary to support long-term preservation (e.g., version) can be indicated. Comments welcome. Human-readable descriptions for the associated files can be provided and are recommended. Conforming readers must provide a mechanism for a user to choose to extract and save (not open) associated files.

See Notes below for use cases and examples that illustrate motivation for adding support for embedded files to the PDF/A-3 standard.