Why Regular PDFs Are Not Enough for Archival
A standard PDF can reference external fonts, link to external files, contain JavaScript, and depend on specific software features to render correctly. While this flexibility is useful for day-to-day work, it creates a problem for preservation: open a complex PDF twenty years from now and it might not display the same way — or at all — if the required fonts are missing, linked resources are gone, or the embedded scripts rely on deprecated features.
PDF/A solves this by defining a strict subset of PDF that is entirely self-contained and designed to be rendered identically far into the future, regardless of the software or hardware used to open it.
The ISO Standard
PDF/A is standardized under ISO 19005. The "A" stands for "archival." Unlike regular PDF (ISO 32000), PDF/A imposes restrictions that guarantee long-term reproducibility. The standard has several parts, each adding capabilities while maintaining the archival guarantee:
- PDF/A-1 (ISO 19005-1:2005) — The original standard, based on PDF 1.4. Requires all fonts to be embedded, prohibits encryption, JavaScript, and external references.
- PDF/A-2 (ISO 19005-2:2011) — Based on PDF 1.7. Adds support for JPEG2000 compression, transparency, layers, and file attachments (as long as attachments are also PDF/A).
- PDF/A-3 (ISO 19005-3:2012) — Same as PDF/A-2 but allows embedding any file format as an attachment (e.g., the original XML invoice data alongside its visual representation).
- PDF/A-4 (ISO 19005-4:2020) — Based on PDF 2.0. Simplifies conformance levels and adopts the latest PDF features.
Each part also has conformance levels:
- Level b (basic) — Guarantees visual reproduction.
- Level a (accessible) — Adds structure tags and Unicode character mapping, enabling text extraction and accessibility.
- Level u (unicode) — All text is in Unicode, enabling reliable search and extraction, but without full structure tags.
What PDF/A Prohibits
To ensure self-containment, PDF/A disallows several features that regular PDFs permit:
- External font references. Every font used in the document must be fully embedded in the file.
- JavaScript. No executable code is allowed.
- Audio and video. Multimedia content is prohibited (it would depend on codecs that may not exist in the future).
- Encryption. The file cannot be password-protected (archival access must not depend on a key that might be lost).
- External content references. No links to external images or resources that might disappear.
- Transparency in PDF/A-1. Transparency was added starting with PDF/A-2.
Who Needs PDF/A?
- Government agencies — Many national archives mandate PDF/A for official records. The U.S. National Archives, European Commission, and numerous courts require or recommend it.
- Legal professionals — Court filings, evidence packages, and long-term legal records benefit from a format that is guaranteed to be openable decades later.
- Healthcare — Patient records, clinical trial documentation, and regulatory submissions often require archival-grade formats.
- Financial institutions — Audit records, tax filings, and compliance documents stored in PDF/A satisfy regulatory retention requirements.
- Libraries and academic institutions — Digital preservation of theses, publications, and historical documents.
PDF/A vs. Regular PDF: A Quick Comparison
- Self-contained — PDF/A: always. Regular PDF: not guaranteed.
- Editable — Both are generally not designed for editing. PDF/A is locked down further.
- Fonts embedded — PDF/A: mandatory. Regular PDF: optional (and often not done, leading to display issues).
- JavaScript — PDF/A: never. Regular PDF: allowed.
- Encryption — PDF/A: never. Regular PDF: allowed.
- Accessibility — PDF/A Level a requires it. Regular PDF: optional.
- File size — PDF/A files are often slightly larger due to mandatory font embedding.
How to Create PDF/A Files
Most professional PDF software can export to PDF/A:
- Microsoft Word — File → Save As → PDF → Options → PDF/A compliant.
- Adobe Acrobat — Use the Preflight tool or "Save as PDF/A."
- LibreOffice — File → Export as PDF → check "Archive (PDF/A-1a)."
- Online tools — Some converters offer PDF/A output. Check that they specify which conformance level (a, b, or u) they produce.
After creating a PDF/A file, you can validate it using tools like veraPDF (open-source) or Adobe Preflight to confirm it meets the standard.
Frequently Asked Questions
Can I convert an existing PDF to PDF/A?
Yes, but it may require embedding missing fonts, removing JavaScript, and flattening transparency. If the source file references external resources that are no longer available, the conversion may not be possible without the original content.
Is PDF/A harder to create than regular PDF?
Not significantly. Most of the restrictions are handled automatically by the export tool. The main difference is ensuring all fonts are embeddable and that the document does not rely on prohibited features.
Can I password-protect a PDF/A file?
No. PDF/A explicitly prohibits encryption. If you need both archival and security, store the unencrypted PDF/A in a secure, access-controlled repository instead.
Will PDF/A files open in any PDF reader?
Yes. PDF/A is a subset of PDF, so any compliant PDF viewer (Adobe Reader, browsers, Preview, etc.) can open it. The viewer simply refrains from executing prohibited features.