PDFA

PDF/A is an ISO standard for the long-term preservation of electronic documents. It is a specialized subset of the Portable Document Format (PDF) intended to ensure that documents can be reliably rendered far in the future, independent of the software, hardware, or operating system originally used to create them. The standard is published as part of ISO 19005 and has developed through several parts: PDF/A-1, PDF/A-2, PDF/A-3, and PDF/A-4.

A core principle of PDF/A is that a file must be self-contained. Documents are required to embed all fonts, define colors using device-independent spaces with embedded ICC profiles, and avoid features that could hinder long-term rendering, such as encryption or external references. The standard also supports metadata and tagging to help future accessibility and discovery.

Conformance levels in PDF/A address different preservation goals. The two widely cited levels are a and b. PDF/A-1a requires tagged content to preserve structure and reading order for accessibility, while PDF/A-1b focuses on faithful visual reproduction. The later parts maintain these conformance concepts while expanding the feature set: PDF/A-2 added support for features like transparency and layers; PDF/A-3 allows embedding of additional files within the PDF; PDF/A-4 updates alignment with newer PDF specifications.

Usage of PDF/A is common among libraries, archives, and government bodies that require durable, reproducible digital records. While it promotes stability, converting existing documents to PDF/A can be challenging, and the restrictions it imposes may limit certain dynamic or protected content.