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.

Digital Preservation Matters.