PDF Versions Explained: 1.4, 1.7, 2.0, and PDF/A

The PDF specification has grown over 30 years. Each revision added features (encryption, compression, transparency, rich media) without breaking existing files. A reader that supports PDF 1.7 can open a 1.4 file, but a 1.4 reader may not understand a 1.7 file. The version in the header is a contract: the file promises it only uses features up to that version.

In practice, modern viewers (Chrome, Firefox, Safari, Adobe Acrobat, macOS Preview, pdf-lib, PDF.js) all support at least PDF 1.7, which is the de facto baseline today. PDF 2.0 is gradually being adopted but most files in the wild are still 1.4–1.7.

PDF 1.4 (2001)

Added transparency (the /ExtGState graphics state), JPEG2000 image support, and tagged PDF for accessibility. This is the baseline for many older print workflows and is still widely produced by older exporters.

PDF 1.5 (2003)

Added object streams and cross-reference streams — the structural compression that lets modern PDFs be much smaller than their 1.4 equivalents. Also added AES-128 encryption (a major security upgrade over the older RC4) and JPEG2000 in object streams. If you compress a PDF and the size drops sharply, you are probably re-saving a 1.4 file as 1.5 with object streams.

PDF 1.6 (2004)

Added AES-256 encryption (the modern default for secure PDFs), improved interactive forms (XFA), and richer annotation support. Most encrypted PDFs you encounter today are 1.6 or 1.7 with AES-256.

PDF 1.7 (2006, ISO 32000-1:2008)

The first version standardized by ISO. PDF 1.7 is thepractical baseline: every modern reader supports it, and most files are written at this level. It clarified 3D artwork, embedded files, and rich media, but the bulk of real-world 1.7 files use only the 1.5 feature set plus a few extras.

PDF 2.0 (2017, ISO 32000-2:2020)

The first version developed under ISO stewardship rather than Adobe alone. It removed deprecated features (RC4 encryption, some legacy name-tree constructs, XFA form architecture was deprecated) and added requirements for real-world robustness: stricter parsing, improved encryption, and better support for transparency and color. PDF 2.0 files are still uncommon because so many writers default to 1.7 for compatibility.

On top of the main version line, several ISO subsets restrict PDF to a specific use case. A file conforming to a subset is still a PDF, but with extra rules.

PDF/A — Archival

ISO 19005, in parts 1–4. PDF/A forbids features that break long-term reproducibility: no encryption, no external references, no JavaScript, fonts must be embedded, color must be device-independent. Used by courts, governments, and archives where the file must render identically decades from now.

PDF/X — Print production

ISO 15930. PDF/X requires all fonts embedded, color in a print color space (CMYK or a named ICC profile), and bleed and trim boxes defined. Used by commercial print shops. Sending a non-PDF/X file to a printer often gets it bounced back.

PDF/UA — Accessibility

ISO 14289. PDF/UA requires a tagged PDF with real reading order, alt text on every meaningful image, a document language, and proper heading hierarchy. Required for WCAG/Section 508 compliance. See ourPDF/UA explainer for the full requirements.

PDF/E — Engineering

ISO 24517. PDF/E supports embedded 3D models and engineering markup. Niche but still maintained.

PDF/VT — Variable & transactional print

ISO 16612. PDF/VT extends PDF/X for variable-data printing — invoices, statements, direct mail where each copy is different. Optimized for high-speed digital presses.

• General sharing: PDF 1.7. Maximum compatibility with no downsides.
• Archiving: PDF/A-2 or PDF/A-3. The archive will outlive the software that made it.
• Commercial print: PDF/X-4 (based on PDF 1.6) or PDF/X-1a (older, PDF 1.3). Ask your print shop which they prefer.
• Accessibility: PDF/UA. Required for government and education in many jurisdictions.
• Encrypted: PDF 1.7 with AES-256. Avoid RC4 (PDF 1.4 and earlier) — it is cryptographically broken.

You usually do not pick the version by hand — your export tool does. Word, Excel, PowerPoint, InDesign, and Acrobat all expose it as a "Save as PDF" option or a preset. The right move is to know which preset matches your destination (Print, Archive, Web) and use it.

Open the file in a text editor and look at the first line. It will read %PDF-1.7 or similar. That is the version declared in the header. For the PDF/* conformance level, you need a tool that reads the OutputIntents andMarkInfo dictionaries — Adobe Acrobat Pro's Preflight is the standard; free alternatives include verapdffor PDF/A and PDF/UA validation.

The version in the header is a lower bound: a file marked %PDF-1.4 can be read by anything that supports 1.4 or later. A file marked %PDF-2.0 may not be read by older tools. When in doubt, save as 1.7.