PDF/A-2: the edition that caught up with the format

In plain words

Written for anybody, with nothing taken for granted. It says what the rule is for and what it changes on the document you end up with.

The first edition was written against a version of the PDF format that was already six years behind by the time documents were being written this way in earnest. Anything the format had learned since — see-through paint, layers a reader can switch off, a newer way of storing photographs — was shut out, not because it threatened the promise but because the text predated it.

So a second edition was published that lets those in, with rules around each of them, and adds a third level between the two the first edition offered.

It also lets a document carry another file inside it, on one condition: that carried file has itself to be archival. That is enough for a set of documents kept as one; it is not enough for an invoice carrying its own figures as a data file, which is what the third edition was written for.

For a developer

The same thing without the detour: the objects, the constraints, and where the line falls between what is produced and what is declared.

The part rests on PDF 1.7, the version published as ISO 32000-1. Transparency, optional content and JPEG 2000 images become allowed, each under its own rules, and a signature may be written in the form the European rules for signatures describe.

Three levels. Level B and level A are what the first edition offered. Level U is new and sits between them: every drawn character maps back to Unicode, so the text can be searched and copied, without the structure hierarchy level A asks for.

A carried file is allowed where that file is itself a document claiming this family. The relationship between the carried file and the page carrying it is stated, so a reader knows what it is looking at rather than guessing from the file name.

Clause by clause

The published text behind each requirement, what the engine measures the document against, and what it leaves to a validator.

This part is not among the claims the engine writes today, and it is planned for a future version. The third edition, which is written today, is this one with a single door opened wider: a carried file may be of any kind rather than archival alone.

A requirement naming the second edition is therefore met in practice by the third, whose text is the same text bar that one clause. An archive that names the edition rather than the family is the case to raise with us: it is the claim, not the document, that is waiting.

The levels of this part

What this part asks for

• Everything the first edition asks for, unchanged.
• Every character drawn maps back to Unicode, at level U and at level A.
• A carried file is itself a document of this family, and the relationship it has to the page carrying it is stated.
• A layer a reader can switch off is named and given a state it starts in.

What this part rules out

A rule that closes a door is what makes the promise keepable: each of these is a way a document could stop being readable later.

• Encryption, programs inside the document, and film or sound.
• Anything fetched from outside the file.
• A carried file of any other kind: a spreadsheet, an image or an invoice's data file needs the third edition.

Where this part stands here today

The claim itself is planned for a future version. The third edition is written today and asks for everything this one asks for, so a document produced here already meets this text.

What every archival document here carries

This holds whichever part is claimed. Nothing on it has to be asked for a second time.

• Every letter the document draws travels inside it, cut down to the shapes the document actually uses, so the page reads the same on a machine where that typeface was never installed.
• A colour statement is written whether or not one was asked for, so the greys and the reds mean the same thing on the next screen as on this one.
• The block that says what the file is — its title, the moment it was written, the part it claims and the year of that edition — is written into the document, and the claim is stated where the part being claimed expects to find it.
• A report can be asked for before anything is written: it comes back with every finding at once, each naming the published text it answers to and the font, layer, page, link, field or cell it is about.
• A document that claimed a part and breaks one of its rules is refused rather than written wrong, and the refusal names the rule.
• Everything the document leads to is inside the document. Every part of the standard allows an instruction opening a file that sits beside it instead; the team declines that instruction under an archival claim, so the document stays readable on its own the day the folder around it is gone. It is the same line the engine already draws on forms.
• Every archival document published on this site is put through two checkers that had no hand in writing it, veraPDF and Ghostscript, and it is their verdict that is shown — not ours.

The requirements, family by family

The eight families below are the same set of requirements for every part, and each of their pages says what comes out on its own and what only you can supply.

• Which part of the archiving standard to claim The archiving standard is a family, not a single rule. Four of its members can be claimed here, and choosing between them takes two questions.
• Every letter the document draws travels inside it A document that carries its own lettering opens the same way on a machine that has never had that typeface installed. That is the first thing the standard asks for, and the one that changes the file most.
• Colours that mean the same thing on every device Numbers on a page are not colours until something says what device they were chosen for. An archival document carries that statement inside it.
• A page that comes out the same for everyone The promise of an archival document is that two readers, twenty years apart, see the same page. That holds only where nothing on the page is left for the reader to settle.
• The document says what its marks stand for A page of ink says where the marks went and nothing about what they mean. The level that is read aloud, and the accessibility standard, ask the document to say it.
• A document that carries other files inside it Part 3 exists because a document sometimes has to carry another file inside it, and that file has to come back out years later, whole.
• What the file says about itself A document kept for thirty years is found again by what it says about itself, not by the folder it happened to be in.
• Checking the claim, before and after Claiming a standard is one line inside the file. What makes the claim worth anything is that something independent agrees with it.

The published texts behind it

Glossary

standard

A rule argued out in committee, published under a number anybody may buy and read, and identical for every firm claiming it. A claim to follow one can therefore be checked against the text. A way of working that merely spread because it worked is a habit of the trade: useful, widespread, and answerable to no text at all.

veraPDF

A free program that checks whether a file really is what it claims to be, against the published rules. It is the tool archives use, so it is the one used here: a document is not called compliant because we say so, but because veraPDF passed it.

attachment

A whole file tucked inside a PDF and carried along with it, the way a paper clip holds a sheet to a folder. Opening the document is enough to get it back out. An electronic invoice works this way: the page a person reads carries the same amounts as a file accounting software reads.

font

The drawing of every letter, digit and mark a document writes, held in a file of its own. A PDF carries the fonts it is set in inside itself, which is why it opens looking the same on a machine that has never had them. Leave them out and a reader puts another font in their place, and the layout moves.

transparency

Paint that lets what is underneath it come back through, by a stated amount. It is what makes a mark laid across a page leave the text under it readable, and a highlight a highlight rather than a blot. The file says how much comes through; whatever draws the page works out the colour that results.

structure tree

The list, held inside a tagged PDF, that says what each part of the page is and what it belongs to: this block is a section, this line its heading, this run of cells one row of that table. It is the shape of the document, kept apart from the ink.

signature

A seal inside the document that proves two things at once: who approved it, and that not one byte has changed since. A reader shows it as a banner at the top of the page.

layer

A named group of things drawn on a page that a reader can switch on and off, like tracing paper laid over a plan. A drawing can hold its measurements on one and its notes on another, and a layer can be set to show on screen and stay off the printer.

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