Every letter the document draws travels inside it

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 typeface is a file, like a photograph. A document may either carry it or name it and hope. Naming it works today, because the machine opening the file happens to own it; it stops working the day nobody does, and the reader puts a different typeface in its place. Line breaks move, a table stops lining up, and a signature block lands on the next page.

So an archival document carries its lettering with it. The file weighs more, and in exchange it is still the same page in thirty years' time. It weighs a good deal less than the whole typeface: only the letters the document actually draws are carried, which for a letter or an invoice is a few dozen shapes out of several thousand.

The text stays text through all of it. Whoever opens the file can still select it, copy it and search it, and so can the software of an archive.

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.

Embedding is automatic and so is subsetting: the drawn glyph set is collected as the pages are laid out, and the shapes and their index tables are rebuilt around it with the glyph indices held stable. The face goes in as a composite font under an identity encoding, with a mapping back to characters written every time, so extraction and search survive the subsetting.

A Type 1 program is carried whole, and a drawn font — one whose glyphs are content streams — counts as carried by construction. Both are accepted under an archival claim and under an accessibility claim.

The fourteen faces a reader is assumed to own carry nothing at all, so a document holding one is refused under either claim, naming the font. The rule reads the document's font table rather than the pages, so a face that was declared and never used refuses the document just the same. Through the rendering service, that is standard_fonts: under archive, use fonts or type1_fonts instead.

Clause by clause

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

Two things a validator looks at are left to the validator. The embedded face keeps its own PostScript name rather than gaining the six-letter prefix that marks a subset, and no list of the glyph numbers kept is written beside it. Neither is measured here.

A character the chosen face has no shape for is drawn as the face's empty box, which the archival and the accessibility standards both decline. The engine does not report it: the chain of fallback fonts is what keeps it from happening.

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.

• Carries the typeface inside the document, without being asked, for every font handed to it.
• Keeps only the shapes the pages actually draw, and rebuilds the tables around them.
• Writes the mapping back to characters every time, so the text stays selectable, copyable and searchable.
• Refuses the document that holds one of the fourteen assumed faces, naming it.

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.

• The typeface file itself, and the right to embed it: a licence is between you and whoever drew the letters.
• A face that covers the characters the document writes, or a chain of faces that between them do.

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.

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.

lightened typeface

Putting into the file only the letters the document actually draws, instead of the whole typeface. A typeface holds thousands of shapes; a letter or an invoice uses a few dozen. Carrying only those is what makes the files here small.

glyph

One drawn shape of a typeface. The letter A is a character; the particular drawing of it that lands on the page is a glyph. The same letter is drawn differently in every typeface.

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.

Type 1 font

The older shape a typeface file comes in, still used where a particular cut of a typeface only ever existed that way. A document carries the file as it was supplied.

Every word the site explains