PDF/A is an ISO-standardized version of the Portable Document Format (PDF) specialized for use in the archiving and long-term preservation of electronic documents (ISO 19005). PDF/A differs from standard PDF by prohibiting features ill-suited to long-term archiving, such as font linking (as opposed to font embedding) and encryption.
The PDF/A Matrix
| Standard | Year | Based On | Key Features |
|---|---|---|---|
| PDF/A-1 | 2005 | PDF 1.4 | No JPEG2000, no layers, mandatory font embedding, mandatory color profiles. |
| PDF/A-2 | 2011 | PDF 1.7 | JPEG2000 support, transparency (layers), embedding of OpenType fonts. |
| PDF/A-3 | 2012 | PDF 1.7 | Allows embedding of any file format (e.g., XML, CSV, CAD) as an attachment. |
| PDF/A-4 | 2020 | PDF 2.0 | Removes conformance levels (a, b, u), simplifies structure. |
Conformance Levels (a, b, u)
Prior to PDF/A-4, standards were divided into conformance levels:
- Level b (Basic): Ensures visual integrity only. The document will look exactly the same when opened years later.
- Level a (Accessible): Requires 'b' plus structure (tags) and Unicode mapping for all text, ensuring the document is machine-readable and accessible to screen readers.
- Level u (Unicode): A bridge between 'b' and 'a', requiring visual integrity and Unicode mapping, but not structural tags.