PDF/A-4: the edition built on PDF 2.0

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.

Three things changed. The letters after the number are gone: there is one plain claim, and what used to be the middle level — every character mapping back to the letter it stands for — is now asked of every document.

Being readable by software that reads a page aloud became a standard of its own rather than a level of this one. A document that needs both claims both, and says so twice.

And the claim is stated in one place instead of two: the block that says what the file is. The older, smaller block that used to repeat it is not written at all.

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 2.0, published as ISO 32000-2. The conformance levels of the earlier parts are gone; what the level U of part 2 asked for is required of every document, and what level A asked for now belongs to the accessibility standard, whose second part is written against the same version of the format.

Two further conformance levels stand beside the plain one. One is for engineering documents and lets a page carry a three-dimensional model; the other is for a document carrying files of any kind, and asks for at least one.

A document of this part carries no information dictionary at all: the claim, the title and the dates are stated in the description block and there alone. Through the rendering service the part is asked for as archive with the value pdfa4.

Clause by clause

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

The plain claim is written today and a request can ask for it by name. The level for carrying files is written by the engine when the document carries one, and is planned for a future version of the request format; the engineering level is planned.

A document claiming this part and refusing one of its rules is refused before a byte is written, and the refusal names the clause. What is published here is then read by veraPDF and by Ghostscript, neither of which had a hand in writing it.

The levels of this part

Each level of this part, and how it is asked for
Level	What it adds	Asked for over the network as
`PDF/A-4`	The page, and every character drawn mapped back to the letter it stands for. There is no letter after the number: this is the whole claim.	`pdfa4`
`PDF/A-4E`	The same, for an engineering document: a page may carry a three-dimensional model of the thing it describes.	Planned for a future version
`PDF/A-4F`	The same, for a document carrying files of any kind. It asks for at least one.	Written by the engine; planned for a future version of a request

What this part asks for

The document header names PDF 2.0.
Every character the document draws maps back to the letter it stands for, with no level to opt out of.
The claim is stated in the description block, naming the part and the year of the edition.
At least one carried file, at the level meant for carrying them.

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 anything fetched from outside the file.
The older description block: the claim is stated once, and a document that states it twice can state it two different ways.
A carried file that is not itself archival, unless the claim is the level meant for carrying files.
A three-dimensional model, unless the claim is the engineering level.

Where this part stands here today

Written today, and asked for by name through the rendering service. The level for carrying files is written by the engine as soon as the document carries one.

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

Each published text, and what it asks for
Published text	What it asks for
`ISO 19005-4 6.1.2`	The version the file header names is the one the part rests on.
`ISO 19005-4 6.1.3`	A document of this part says what it is in its description block and there alone.
`ISO 19005-4 6.2.10.4.1`	Every typeface the document draws with is carried inside the file.
`ISO 19005-4 6.2.7.1`	What a reader is to do between an image's samples is stated, not left to it.
`ISO 19005-4 6.6.1`	Which kinds of action a document of this part may hold.
`ISO 19005-4 6.9`	A document at the level for carrying files names the files it carries.
`ISO 19005-4 6.10`	What a set of layers a reader can switch off has to declare.

The other editions of the standard

PDF/A-1 PDF/A-2 PDF/A-3

Back to what the archiving standard asks for

See the prices See the examples

Glossary

byte: The unit a file's weight is counted in, the way a parcel is counted in grams. A thousand of them make a kilobyte, and a million make a megabyte — the size of one photograph taken with a telephone. A one-page PDF here weighs between six thousand and a hundred and twenty thousand, so a hundred of them fit in the space of five photographs.
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.
request: One call to the service: you send what the document should say, and get the document back. Your bill counts these calls, one for each document. The number of pages inside a document is never counted.
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.

Every word the site explains