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PDF/A Family, PDF for Long-term Preservation

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name ISO 19005. Document management - Electronic document file format for long-term preservation
Description

PDF/A is a family of ISO standards for constrained forms of PDF (see PDF_family) intended to be suitable for long-term preservation of page-oriented documents for which PDF is already being used in practice. The PDF/A standards are developed and maintained by a working group with representatives from government, industry, and academia and active support from Adobe Systems Incorporated. The working group is WG 5 of Technical Committee ISO/TC 171, Document management applications, Subcommittee SC 2, Application issues [ISO TC171/SC2/WG5]. This group works in cooperation with: ISO/TC130, Graphics technology; ISO/TC42, Photography; and ISO/TC46/SC11, Information and documentation, Archives/records management.

PDF/A-1, the first PDF/A standard [ISO 19005-1:2005], was based on PDF version 1.4 (see PDF-1-4) and published in 2005.

PDF/A-2 as defined in ISO 19005-2:2011, extended the capabilities of PDF/A-1 and is based on PDF version 1.7 (as defined in ISO 32000-1, see PDF-1-7). One new capability was to allow the embedding of PDF/A-compliant attachments.

PDF/A-3 added a single and highly significant feature to its predecessor (PDF/A-2), to permit the embedding of a file or files in any format. The intent expressed by many proponents is that the embedded files not be considered part of the archival payload. However, use cases are emerging where the embedded files would likely warrant preservation by archival institutions.

The primary distinction between PDF/A-1 and PDF/A-2 is that they are based on different chronological versions of PDF. A new version of PDF/A based on PDF 2.0 is under development as PDF/A-4. Plans were described in The Future of PDF/A and Validation, a presentation from 2017, in which the name PDF/A-Next is used.

The primary purpose for the PDF/A format is to represent electronic documents in a manner that preserves their static visual appearance over time, independent of the tools and systems used for creating, storing or rendering the files. To this end, PDF/A attempts to maximize device independence, self-containment, and self-documentation.

The constraints for PDF/A-1, PDF/A-2, and PDF/A-3 include:

  • Audio and video content are forbidden. 3D artwork is also forbidden.
  • Javascript and executable file launches are prohibited.
  • All fonts must be embedded and also must be legally embeddable for unlimited, universal rendering.
  • Colorspaces must be specified in a device-independent manner.
  • Encryption is disallowed.
  • Use of standards-based metadata is mandated.

The first three PDF/A standards define levels of conformance that are similar.  In ISO standards 19005-1, 19005-2, or 19005-3 (for PDF/A-1, PDF/A-2, and PDF/A-3, respectively), conformance level A satisfies all requirements in the standard; level B and level U are lower levels of conformance, still satisfying the requirements regarding the visual appearance of electronic documents, but less demanding as to representation of structural or semantic properties.  For example, level B conformance is the level typically used for PDF/A files created from scanned pages.  Although the terminology is not used in the ISO standards, the PDF Association, in its 2013 document PDF/A in a Nutshell 2.0, introduced the terms Accessible, Basic, and Unicode to describe the three conformance levels. However, a PDF/A file conforming to level A does not necessarily conform to the PDF Enhancement for Accessibility standard (PDF/UA