PDF library

What the word means

It is not a program you open. There is no window, no menu and nothing to click: it has no face at all. It waits inside a program somebody at your firm wrote, and that program is what tells it to put this title here, that table there, this logo in the corner. What comes back is the finished file.

Four words are used on this site, and two of them mean the same thing. The library and the engine are one object under two names. The server is a second program: it holds the engine and answers whoever asks it for a document over the network, so the program asking never has to hold the engine itself. The rendering service is that same server, running on our machines instead of yours.

What it does on a real document

A firm that bills its customers already has the amounts, in the software it runs its business on. What it does not have is the invoice as a file: a page laid out, with the letterhead, the table of lines, the totals and the code that pays it. Writing that by hand means learning how a PDF file is put together, which is a job of months.

The library is that job, done once and sold ready. Somebody who writes programs where you work spends a day connecting it to the figures you already hold, and from then on every invoice comes out on its own.

Where it comes from, and why

The PDF format was published as a specification anybody may read, and it runs to well over a thousand pages. Everything a page can hold is in there — lettering, colour, pictures, boxes to fill in, seals, rules for files that must still open in twenty years.

Nobody reads all of it to print an invoice. That is why libraries exist: one team reads the specification so that everybody else does not have to.

See it on a finished document

A commercial invoice A payslip The rules behind this word, and the texts they are read from