PDF internals
The parts of the PDF format that decide whether an edit works — written by the people who implement them, with the file that proves it.
Five things worth understanding
Most explanations of PDF editing are written by people who have never had to make it work. These are the five details that actually decide whether your document survives an edit — and each one names the code in our own editor that handles it, so you can hold the claim to account.
Content streams
A PDF content stream is the ordered list of operators inside a page object that draws that page’s text, images, and vector graphics at fixed coordinates.
Read it →Incremental updates
A PDF incremental update is an edit saved by appending only the modified objects and a new cross-reference section to the end of the existing file, leaving all prior bytes intact.
Read it →Font subsetting
Font subsetting is the practice of embedding only the glyphs a document actually uses, rather than the entire typeface, to keep the PDF small.
Read it →Per-glyph text
Per-glyph text is PDF content where each character is drawn by its own positioned operator instead of being grouped into word- or line-level text runs.
Read it →Cross-reference tables
A PDF cross-reference section is the index at the end of a PDF that records the byte offset of every object, letting a reader locate objects directly.
Read it →
Want to see it rather than read it? Open the editor — the before/after on that page is generated by running this pipeline against a real invoice, and it measures what changed.