Saturday, May 11, 2013

PDF/A, PDF for Long-term Preservation.

PDF/A, PDF for Long-term Preservation. Library of Congress.  March 21, 2013.
This section on PDF/A is part of the Library of Congress website on sustainable formats. The page includes description of PDF/A, sustainability factors, quality and functionality factors, format specifications, and useful references.

PDF/A is a family of ISO standards that attempt provide sustainable formats, through device independence, self-containment, and self-documentation. 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.

PDF/A-1, the first PDF/A standard, was based on PDF version 1.4 and published in 2005.
PDF/A-2 extends the capabilities of PDF/A-1 and is based on PDF version 1.7.
PDF/A-3 allows including in a PDF/A file, other types of files in any other format, not just other PDF/A files.

Restrictions on PDF/A files include:
  • Audio and video content are forbidden
  • Javascript and executable file launches are prohibited
  • All fonts must be legally embeddable for unlimited, universal rendering
  • Colorspaces specified in a device-independent manner
  • Encryption is disallowed
  • Use of standards-based metadata is mandated
The PDF/A standards define levels of conformance: conformance level A satisfies all requirements in the specification; level B and level U are lower levels of conformance, still satisfying the requirements of ISO 19005 regarding the visual appearance of electronic documents, but less demanding as to representation of structural or semantic properties.

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