What is PDF/A, and when do you need it?
· 6 minute read
PDF/A is the version of PDF built to last. What it guarantees, the difference between PDF/A-1 and PDF/A-2, and how to convert an ordinary PDF.
Sooner or later someone asks for a document "in PDF/A", usually a court, a registry, a university or an archive. It looks like an ordinary PDF and opens in the same programs. The difference is in what the file promises about the future.
The problem it solves
An ordinary PDF can quietly depend on things that are not inside it. It may use a font that is installed on the author’s computer but not embedded. It may assume a colour setting that the viewer supplies. It may link to something on the web, or contain a script, or an audio clip. Open it in ten years on a different system, and any of those dependencies can fail: the text reflows in a substitute font, colours shift, a link goes nowhere.
PDF/A, where the A stands for archival, takes away every one of those dependencies. A PDF/A file has to contain everything it needs to look the same in the future.
What a PDF/A file must do
- Embed every font it uses, so the text looks as it did.
- Define its colours in a way that travels with the file, rather than relying on the viewer.
- Avoid features that depend on the outside world: external links to content, scripts, embedded audio and video.
- Not be encrypted. A document you cannot open without a password cannot be reliably preserved.
- Carry its descriptive information in a standard form, so that archives can index it.
PDF/A-1 or PDF/A-2?
There are several parts of the standard. PDF/A-1 is the oldest and strictest, and it is built on an older version of PDF, which means it does not allow some things that modern documents contain, such as transparency. PDF/A-2 is based on a newer version of PDF and permits more of what modern documents use, while keeping the same guarantees.
The practical rule is simple. If whoever asked for the document specifies a part, use that one. If they do not, choose PDF/A-2. Pick PDF/A-1 only when a system or an authority requires it.
Converting an existing PDF
The best way to get a PDF/A is to export one from the program that created the document, since that program knows what it used. If you only have the finished PDF, you can convert it. The conversion embeds fonts, fixes the colour definition and removes forbidden features.
- If the file is protected with a password, take it off first with Unlock PDF, because PDF/A does not allow encryption.
- Convert a copy, not your only file.
- Open the result and check that the pages look as they did.
- If a court or registry will validate it, check it with a validator first. A conversion aims to conform but is not a certificate.
What to expect
The file is usually larger, because it now carries its fonts and a colour profile. Some features are flattened or dropped, such as video, scripts and some transparency effects. If size matters, Compress PDF can reduce it, though you should re-check conformance afterwards if it must be strictly validated.
Tools mentioned
- PDF to PDF/A — The archival form, with everything it needs embedded in it.
- Protect PDF — A password on the file before it leaves your hands.
- Unlock PDF — Take the password off a file you own.
- Compress PDF — A smaller file that still reads like the original.