PDF 32000-1:2008 — The PDF Specification
TL;DR — The full ISO specification for PDF 1.7 — 756 pages defining the format this entire collection is made of.
⬇ Download the archived copy — kept here so the document survives its source going dark. Explicitly free / author-released / CC.
PDF 32000-1:2008, First Edition, 1 July 2008. Document management — Portable document format — Part 1: PDF 1.7.
The format’s complete specification: object model, document structure, graphics, text and fonts, rendering, interactive features, and the encoding of everything else.
There is a pleasing recursion in a library of PDFs containing the definition of a PDF. Practically, it is the document you need open when a file will not parse and you have to find out why.
Where this came from
756 pages. A copy is archived locally against link rot; the header links the original source.