A Plain-English Glossary of Common PDF Terms

Searching for PDF-related help constantly runs into a pile of technical jargon, and any single term in isolation is easy to half-understand. This glossary covers the most common concepts in one place, each with a plain-English explanation.

AcroForm (interactive form)

The real, clickable form-field system built into a PDF — a completely different thing from a scanned form that only looks like a table but is really an image. See our PDF forms article.

Tags (tag structure)

Structured information that tells a screen reader "this is a heading," "this is body text," "this is an image" — it directly determines whether a PDF is usable for blind users. See our PDF accessibility article.

Rasterize

The process of converting vector text or graphics into a pixel-based image. Once rasterized, text is no longer "text" — it can't be selected, searched, or copied. A scan is essentially a whole page that's been rasterized.

Flatten

"Baking" interactive form fields or an annotation layer into the page's static content, after which those elements can no longer be individually selected or edited. Commonly used once a form is filled out and finalized.

OCR (optical character recognition)

Detecting the text inside a scanned document (which is really just an image) and converting it into a genuine selectable, searchable text layer — reversing the "text became an image" problem caused by rasterizing.

Metadata

Information embedded inside a file that doesn't show up directly on the page — author, creation date, and similar. See our article on reading a PDF's metadata.

Bookmark / outline

The clickable table-of-contents structure in the sidebar, used to quickly navigate a long document. See our article on how PDF bookmarks and navigation work.

Font subsetting

Embedding only the glyph data for the characters actually used in a document, instead of an entire font file — avoiding the huge size increase a full font embed would cause. See our article on the role of fonts in PDF files.

Linearized (Fast Web View)

Reorganizing a file's internal data order so a reader can display the first page while the rest is still downloading, instead of waiting for the whole file. See our article on what linearized PDF means.

PDF/A

A stricter variant built for long-term archiving, requiring every resource to be self-contained inside the file. See our PDF/A explainer.