PDF toolsA normal PDF can contain almost anything: fonts that aren't embedded, colours defined loosely, scripts, links to external files. That freedom is convenient and, for some uses, a liability. The lettered standards are subsets of PDF that forbid the risky parts and require the useful ones.
PDF/A: for archiving
PDF/A (ISO 19005) exists so a document can still be opened and displayed correctly in decades. It requires everything needed to render the page to be inside the file, and bans anything that depends on the outside world or could change.
- All fonts must be embedded.
- Colours must be defined in a device-independent way.
- No encryption, no JavaScript, no audio or video, no links to external content needed for display.
There are several parts. PDF/A-1 (2005) was based on PDF 1.4. PDF/A-2 (2011) moved to the ISO version of PDF and allowed transparency and layers. PDF/A-3 (2012) allows other files to be attached, which is how some e-invoice formats carry machine-readable data inside a human-readable PDF. PDF/A-4 (2020) is based on PDF 2.0. Letters after the number, like PDF/A-2b, are conformance levels: "b" means the visual appearance is preserved, "a" adds requirements for structure and accessibility, "u" requires text to be mapped to Unicode.
Courts, public archives and many government portals ask for PDF/A. Most word processors can export it: look for a "PDF/A" or "archive" checkbox in the PDF export options.
PDF/X: for printing
PDF/X (ISO 15930) is the print industry's standard. Its job is to make sure what comes off the press matches what the designer approved. Fonts must be embedded, colours must be suitable for printing (with an "output intent" describing the target press), and the page boxes that define trim and bleed must be set. Common versions are PDF/X-1a, PDF/X-3 and PDF/X-4. If a print shop asks for one, export it from your design software; it isn't something to add afterwards.
PDF/UA: for accessibility
PDF/UA (ISO 14289) is about people who use screen readers and other assistive technology. A PDF/UA file is fully tagged: headings, paragraphs, lists, tables and figures are marked up, images have text alternatives, reading order is defined. PDF/UA-1 dates from 2012; PDF/UA-2, based on PDF 2.0, was published in 2024. Our accessible PDF checklist covers the practical side.
PDF/E: for engineering
PDF/E (ISO 24517) targets engineering and technical documents, including drawings with layers and 3D content. You're unlikely to need it unless you work in construction or manufacturing.
Can a file be several at once?
Yes. A file can conform to PDF/A and PDF/UA at the same time, for example, and archives of public documents increasingly ask for both.
A note on our tools
Tools that rewrite a PDF, including ours, don't guarantee the output still conforms to these standards. If you must deliver PDF/A or PDF/X, make the final export from the original software and do any merging or page editing before that step.