If you have ever exported a PDF and been asked to choose between PDF/A, PDF/X, or some other letter, you are not alone in finding it confusing. These are not marketing names — each is a separate ISO standard built for one specific job. Picking the right one takes thirty seconds once you know what they are for; picking the wrong one can mean a print shop rejects your file or an archive fails a compliance check.
Here is the plain-English version of the PDF standards that actually exist, and how to tell which you need.
The short answer
Most people never need a specialized PDF at all — a standard PDF is fine for sharing and reading. You only need a sub-standard when a specific system requires it: long-term archiving, commercial printing, engineering, or accessibility. If that is you, here is the map.
PDF/A — for archiving and long-term storage
PDF/A (ISO 19005) is built so a document looks the same in fifty years as it does today. It requires everything the file needs to be embedded inside it — fonts, colour profiles, images — and forbids anything that depends on the outside world or could change later: no encryption, no audio or video, no JavaScript, no links to external files.
Use it when: you are keeping records that must stay readable and unaltered — legal documents, financial records, government filings, anything with a retention requirement. Later versions (PDF/A-2 and A-3) relax a few rules; A-3, for example, lets you attach the original source file inside the PDF.
PDF/X — for commercial printing
PDF/X (ISO 15930) exists so the file you send to a print shop comes out with the right colours and fonts every time. It locks down colour information so a red stays the correct red on press, and it requires fonts to be embedded, removing the guesswork that causes costly reprints.
Use it when: you are sending artwork to a professional printer — brochures, packaging, magazines. If a printer asks for a “print-ready PDF,” PDF/X is usually what they mean.
PDF/E — for engineering and technical drawings
PDF/E (ISO 24517) is designed for engineering workflows — CAD drawings, schematics, and documents that may include interactive 3D models. It is a niche standard, but the right one when you are exchanging technical drawings that need to preserve precise geometry.
Use it when: you work with CAD or engineering documentation and need a portable, faithful copy of a technical drawing.
PDF/UA — for accessibility
PDF/UA (ISO 14289) makes a PDF usable with assistive technology such as screen readers. It requires the document to be properly “tagged” so its structure — headings, reading order, and alternative text for images — is machine-readable.
Use it when: you publish documents that must be accessible — public-sector material, anything covered by accessibility law, or simply documents you want everyone to be able to use.
A quick note on “PDF/B” and “PDF/Z”
If you have seen guides referencing a “PDF/B” or “PDF/Z” standard, those do not exist. The official ISO PDF sub-standards are PDF/A, PDF/X, PDF/E, PDF/UA, and PDF/VT (a specialist standard for high-volume personalized printing). There is no point converting a file to a format that no software actually supports.
Which one should you pick?
- Keep a document readable for years, or meet a compliance rule → PDF/A
- Send artwork to a print shop → PDF/X
- Share CAD or engineering drawings → PDF/E
- Make a document screen-reader accessible → PDF/UA
- Just emailing or sharing a file → a standard PDF is fine
The honest takeaway
Unless a printer, an archive system, or an accessibility requirement is telling you otherwise, you almost certainly just need a normal PDF. The specialized standards solve real but specific problems — and the moment you know which problem you have, the choice makes itself. When you do need to convert, target only the real standards above.