PDF/A: The Long-Term Archiving Format Explained
PDF/A is a standardized version of PDF built for a single mission: to guarantee that a document stays readable and true to the original for decades. Where an ordinary PDF may depend on fonts or external resources, a PDF/A embeds everything it needs to always display the same way. This guide explains what the format really is, why it exists, and how to obtain a compliant file.
What is PDF/A?
PDF/A is a subset of the PDF format dedicated specifically to long-term digital archiving. It is defined by an international standard published by ISO under the reference ISO 19005, which means its rules are set publicly and independently of any single software vendor. A PDF/A file therefore remains a PDF that any reader can open, but it follows extra constraints that guarantee its stability over time.
The core idea is self-sufficiency: a PDF/A document must contain within itself all the information needed to display it, never relying on external elements that could disappear. It is not a different format that your recipients would have to install, but a more rigorous way of producing a PDF, designed for preservation rather than fast exchange.
Why does PDF/A exist?
A document meant to be kept for a long time faces a quiet enemy: the evolution of technology. A font installed today may be missing tomorrow, a link to an image stored elsewhere can break, and software may stop interpreting a feature that has become obsolete. The result is that a PDF opened in ten or twenty years may render differently, or even become unreadable. PDF/A was created precisely to remove that risk.
The goal is identical, reproducible rendering over time: whether the file is opened today or in several decades, on an operating system not yet invented, it must present exactly the same visual content. To achieve this, the standard requires the document to be complete and deterministic, with no grey areas and no dependency that could alter its future appearance.
How does PDF/A differ from a normal PDF?
The most visible difference concerns fonts: a PDF/A must embed every font used, including the most common ones. That way, even if the original font no longer exists on the machine opening the file, the text still appears exactly as designed. Likewise, colors are described in a device-independent way, through embedded color profiles, so that hues do not shift from one screen or printer to another.
PDF/A also forbids everything that makes a document unpredictable or dependent on the outside world: no JavaScript or active content, no encryption or password protection, and no references to an audio file, video, or remote resource. Metadata must follow a standardized format too, which makes documents easier to index and identify inside an archive; the metadata tool helps you check and clean up this descriptive information.
Conformance levels: PDF/A-1, 2, 3 and a, b, u
The standard has grown in several parts. PDF/A-1 is the original, strictest version, based on an older generation of PDF. PDF/A-2 modernized the format by allowing useful features such as JPEG 2000 compression, transparency, and embedded PDF/A files. PDF/A-3 builds on PDF/A-2 but additionally lets you attach any source file to the document, for example a data-format invoice alongside its printable version.
Each version then comes in conformance levels marked by a letter. Level b (for basic) guarantees only visual fidelity: the document will always look the same. Level a (for accessible) adds a logical structure and tagging that make the content accessible and easy to extract, notably for screen readers. Level u (for unicode), available from PDF/A-2 onward, sits in between: it ensures that all text is mapped to reliable Unicode, enabling accurate searching and copy-paste.
Who needs PDF/A and how do you create one?
PDF/A is aimed at anyone who must retain documents in a durable, defensible way: government bodies and public services bound by legal archiving duties, legal professionals handling deeds and case files, libraries and heritage institutions digitizing collections, and also companies subject to compliance requirements for their invoices, contracts, or regulatory reports. In many of these contexts, PDF/A is explicitly required.
To obtain a compliant file, the simplest route is to convert an existing PDF with the pdf-to-pdfa tool: it embeds the fonts, adds the required color profiles, and removes forbidden elements to produce a valid document. If your source file is large, you can first slim it down with the compress tool, keeping in mind that embedding fonts can slightly increase the final size. Once converted, review its descriptive information with the metadata tool for clean, well-identified archiving.
Frequently asked questions
What is the difference between PDF/A and PDF?
PDF/A is a PDF subject to extra rules for archiving: embedded fonts, device-independent colors, and a ban on external or active elements. A regular PDF is more flexible but may render differently over time, whereas a PDF/A aims for identical rendering across decades. Every PDF/A stays readable in any PDF reader.
Can you edit a PDF/A?
Yes, technically nothing prevents you from editing a PDF/A, but any change may break its conformance, for instance by adding a non-embedded font or forbidden content. The good practice is to make your edits and then re-convert the document to PDF/A to ensure it meets the standard again.
Does PDF/A increase file size?
Often a little, because it embeds all fonts and color profiles, which makes the document heavier than a PDF that would rely on external resources. The increase is usually moderate. If size is an issue, the compress tool can reduce a file before conversion.
Which PDF/A level should I use?
Level b is enough if your only goal is long-term visual fidelity. Choose level u to preserve reliable text search and copy-paste, and level a when accessibility and a logical structure are required. As for the version, PDF/A-2 suits most needs; PDF/A-3 is useful when you must attach a source file to the document.