Treat PDF as one blob and you’ll hit edge cases forever. Learn the family tree and most mysteries disappear.
PDF the format vs. PDF the standards
The core PDF specification evolved from version 1.0 (1993) to the current ISO 32000-2 (PDF 2.0). On top of the core, specialised standards tighten the rules for particular use cases.
Core PDF versions
- 1.4 (2001) — transparency, 128-bit RC4, JavaScript.
- 1.5 (2003) — object streams, cross-reference streams, JBIG2.
- 1.6 (2004) — embedded 3D, OpenType font support.
- 1.7 (2008) — becomes ISO 32000-1; AES-128 encryption.
- 2.0 (2017, revised 2020) — ISO 32000-2; AES-256, GeoPDF, improvements across the board.
PDF/A — Archival
Flavours: 1a/1b (ISO 19005-1, 2005), 2a/2b/2u (2011), 3a/3b/3u (2012), 4/4e/4f (2020). Pick 2b for most archives, 3u if you need embedded source files, 4 for post-2020 archival with Unicode normalisation.
PDF/X — Prepress
For print output. Common flavours: PDF/X-1a (CMYK only), PDF/X-3 (CMYK + spot + ICC), PDF/X-4 (transparency + layers), PDF/X-5n (n-colorant). Printers usually tell you which they want.
PDF/UA — Accessibility
ISO 14289. Requires tagging, language declaration and more. See our accessibility article.
Which to pick?
If you’re distributing to anyone with a modern Reader, PDF 1.7 or 2.0 is fine. If anybody will archive it, pick a PDF/A profile. If it’s going to a printer, ask for PDF/X-4. For public-sector or regulated audiences, add PDF/UA tags on top.
Checking conformance
Open-source: veraPDF (free, accurate). Commercial: callas pdfToolbox, PitStop. All three can validate PDF/A and PDF/UA; the first two also validate PDF/X.
Keep learning
The ISO 32000-2 specification is now free to download at ISO.org. Grab it, bookmark the Table of Contents, and keep it next to your coffee. You’ll surprise yourself with how often it answers a weird PDF question.
Tags: #PDF standards #PDF/A #PDF/X #PDF/UA #PDF 2.0
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