A page that comes out the same for everyone

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.

A PDF is allowed to leave decisions to whatever opens it. A group of drawings can be told to show on screen and stay off the printer. A picture can ask to be smoothed over, and each reader smooths differently. A clickable area can be there and invisible. A page can be told to do something the moment somebody arrives at it.

None of that is a fault in one program or another: the format allows it, which is exactly why the archiving standard had to be written. An archival document settles all of it inside the file, so the page a reader gets is the page that was meant.

What this costs in practice is small. Groups of drawings are still allowed — what goes is the instruction that switches them on and off by itself. Clickable links are still allowed — they simply have to be visible and printable. Buttons that run something when pressed belong to a living document rather than an archived one.

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.

Optional content is permitted; automatic state is not. A layer whose visibility follows printing, the screen, the magnification or the reader's language refuses the document. The layer itself, and the default configuration naming it, are written as usual.

An image is drawn from the samples it carries: interpolation refuses the document. Every annotation is printed and none is invisible, hidden or kept off the screen either way — form widgets are written printed by construction, so the rule bites on shapes and links.

Actions are judged on their type, never on where they lead. Part 3 permits going to a page of this document, to another document, to a document carried inside this one, to a reading thread, to an address on the web, and to a place this document registers under a name, plus submitting a form. Part 4 permits those and three more: running a script, playing a media item the file carries, and going to one of the parts a document is divided into. Beyond the type: a field that acts when it is used refuses the document under every part; a field that acts when something happens to it refuses it under part 3 and is allowed under part 4; a page that acts on arrival or departure refuses it under both.

A claimed document is written with at most 8 388 607 objects, and is refused above that, which is the standard's own ceiling rather than the format's.

Clause by clause

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

Three things the standard settles are left to a validator. A claimed document that also asks for a password is written as asked, and a validator declines it — an archival document is written without one. Transparency, soft masks and blend modes are written as asked and measured by nobody here. And the additional actions of the document itself, as opposed to those of a page, are not read.

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.

• Names the default configuration of the layers, which the standard asks for and which nobody would think to ask for.
• Writes every form widget as printable.
• Refuses the document over a layer with automatic state, a smoothed image, a hidden or unprintable link or shape, a forbidden kind of action, a field or page that acts, and a document past the object ceiling — naming, in each case, which one.

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.

• Layers without automatic state: name them, draw on them, and leave their visibility to the reader.
• Images asked for without smoothing.
• Links and shapes left visible and printable.
• A document without a password, and without transparency where the receiving archive declines 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.

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.

annotation

Something laid over a page rather than drawn into it: a clickable rectangle, a box to type in, a button. It sits at its own place on the sheet and is what makes a PDF answer to a click at all.

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.

Every word the site explains