Checking the claim, before and after

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.

There are three moments. Before the file is written you can ask whether what you have composed would be taken, and get back a list of everything that stands in the way, all at once. When the file is written, a document that claimed the standard is refused rather than written wrong. And once it exists, a free program that has never heard of us opens it and answers pass or fail.

The third one is the one that counts. A document is not compliant because the firm that wrote it says so. It is compliant because veraPDF, run by two bodies whose business is keeping documents readable and in which the team owns no part, opened it and accepted it.

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 report is asked for on the document as composed. Nothing is written and nothing is changed, and the document need not have claimed anything: the question is whether it would be taken. Each finding names the published text, what stands in the way, and what it is about — which font, which layer, which page, which link, which field, which cell.

The refusal at write time runs the same rules and stops at the first, for a document that actually claimed. Rules that ask for something missing — a tree at level A, a carried file at the level for carrying files — are refused separately and say what is missing rather than what is in the way.

A file the engine did not write can be read and reported against the same clauses. That report also lists what it did not read, and says why: what a link, a field or a page does when it is used is not followed, and the description packet is handed back as bytes rather than interpreted. Reading a document walks the resources of its pages, following nested drawings sixteen deep and stopping after 4 096 resource dictionaries.

Clause by clause

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

An empty report is not a certificate. What the engine does not know to look for, it does not report, and it never calls a document conforming: conformance is what a validator that did not write the file says.

What it does not look for, stated plainly so nobody counts on it: a password on a claimed document; the paint measured against the colour statement; transparency and blend modes; the contents of a carried file; the description packet itself; the additional actions of the document as opposed to those of a page; the marking of decoration; and a character the chosen face has no shape for. Each of those is a validator's to catch.

One difference between the two readings is worth knowing. Writing judges the document's font table, so a face declared and never used refuses the file; reading judges the fonts the pages actually name, so a font nothing selects is passed over.

What the engine does on its own

Nothing on this list has to be asked for. It comes out of a document that claims the standard, whatever else the calling program says.

Reports everything it knows to look for at once, before anything is written, naming the published text and the subject of each finding.
Refuses to write a document that claimed a standard and breaks one of the rules above, naming the first.
Reads a file it did not write and reports against the same clauses, listing what it left unread and why.

What you supply

Nothing on this list can be guessed. The engine states what it was given and declines to invent the rest, which is why the document is refused rather than written with a value nobody chose.

Asking for the report: it is not run behind your back.
The validator's verdict, on the file that will actually be kept, which is the only verdict an archive accepts.
Everything on the list above that nothing here measures, chief among them the agreement between the paint and the colour statement.

The other families of requirements

Which part of the archiving standard to claim Every letter the document draws travels inside it Colours that mean the same thing on every device A page that comes out the same for everyone The document says what its marks stand for A document that carries other files inside it What the file says about itself

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.
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.
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.
blend mode: The rule for what happens to the colour where one mark is laid over another: covered up, darkened, lightened, multiplied. The plain rule is that the top one wins.

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