The words of the PDF format, in plain language
Every word on this list turns up somewhere on this site, and every one of them is explained here rather than assumed known.
Each has a page of its own: what the word means, what it does on a real document, and why anybody invented it in the first place.
Wherever one of these words is written in a sentence on this site, it is a link, and the link leads here.
- PDF/A
- A PDF made to be readable in twenty years' time. Everything it needs is inside the file — the fonts, the colours, the description of what it is — so nothing it depends on can go missing later. Public bodies and archives ask for it by name.
- PDF/UA
- A PDF a blind reader can use. The file itself says which text is a heading, which is a paragraph, and in what order the software that reads a page aloud should say it all. Without that, the software reads the page in the order it was drawn, which is rarely the right one.
- 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.
- Factur-X
- An invoice that is a page for a person and a data file for a machine, in one document. The page looks like any invoice; inside, the same amounts are attached in a form accounting software reads without anybody retyping them. French law requires this exchange between companies.
- XMP
- The block inside a file that says what the file is: its title, who made it, when, and which rules it follows. Search engines and archives read it; a reader never sees it.
- colour profile
- A file that says what a colour actually looks like. Without one, the same red is one red on your screen and another on a press. A document meant for print carries the profile its colours were chosen against.
- output intent
- The colour profile written into a document to say which press or which screen its colours were chosen for. A printer reads it to know what the numbers in the file are meant to look like, and the rules on documents kept for the long term ask for one.
- PDF/X
- A PDF a printing works can put straight on the press without asking anybody anything: the colours are stated in a way the press understands, the lettering is inside the file, and the page says where the blade cuts and how far the ink runs past it.
- CMYK
- The four inks a printing press lays down: cyan, magenta, yellow and black. A screen mixes light instead, so a document going to a press states its colours in inks, not in screen colours.
- subset
- 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.
- tagged PDF
- A PDF that carries the structure of its own text alongside the drawing: this is a heading, this is a table, this cell belongs to that column. It is what lets a reading aid, or a program pulling data back out, make sense of the page.
- 2D barcode
- A code read in two directions at once, so it holds far more than the striped kind: a web address, a payment, a whole delivery line. A phone camera reads one without any special equipment.
- QR code
- The square of black and white dots you point a phone at: on a poster, on a restaurant table, at the foot of a bill. It carries a web address, or the exact details of a payment, so nobody has to type anything in. On an invoice it turns paying into one tap.
- DataMatrix
- A tiny square code, sometimes smaller than a grain of rice, for things with no room for anything bigger: a box of medicine, an electronic part, a parcel. It is still read when a corner of it is scratched or smudged, which is why factories and pharmacies print it.
- Aztec
- The code with a little target in the middle, the one on a train ticket or on a boarding pass held up on a phone screen. It was made to be read off a lit screen and through a scratched window, and it takes less room than the others for the same text.
- PDF417
- A wide, flat code made of stacked bars, the one on the back of a driving licence, on an airline boarding pass or on a shipping label. It holds several hundred characters — a whole identity, a whole delivery line — where an ordinary striped code holds a number.
- 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.
- binding
- The way one language uses code written in another. The engine is written in Rust; the Python binding is what lets a Python program call it as if it had been written in Python.
- API key
- A long secret string your program sends with each request so the service knows the request is yours. It stands in for a password, and is never shown to anybody who visits a page.
- request
- One call to the service: you send what the document should say, and get the document back. What is counted for billing is these calls, and the pages they produced.
- template
- A PDF file made once and reused as the background of new pages: your letterhead, a plain sheet for the pages that follow, the page of terms you always attach at the end. Nothing on it is redrawn — the file is laid down as it stands, and the new text is written on top.
- watermark
- Wording printed across the page itself, saying the document was made with a free account. It cannot be removed from the file; a paid tier simply never puts it there.