PDF Glossary: Common Terms Explained

PDF tools use a lot of jargon. This glossary explains the terms you are most likely to meet, with practical notes on when they matter.

By the Easy PDF Tool team at Digimarket Group SIA · Updated 4 November 2026

PDF

Portable Document Format, created by Adobe in the early 1990s and now an open ISO standard (ISO 32000). It describes pages so they look the same on any device.

PDF/A

An archival version of PDF that embeds fonts and forbids features that might not display in future. Often required for long-term records and some court or government filings.

OCR (optical character recognition)

Software that recognises text in images, making a scanned PDF searchable and copyable. Without OCR, a scan is just pictures of text.

DPI (dots per inch)

Resolution of a scan or image. 150–200 dpi is usually enough for on-screen documents; 300 dpi is common for print.

Compression

Reducing file size, mostly by resampling and re-encoding images. Lossy compression discards some detail.

Flattening

Merging form fields, annotations and layers into the page content so they can no longer be edited and display consistently everywhere.

Redaction

Permanently removing sensitive content. Drawing a black box over text is not redaction — the text can often still be copied. Use a real redaction feature, then check by searching for the removed words.

Metadata

Information stored about the file, such as title, author, software and dates. Check it before publishing documents.

Encryption / password protection

An “open password” prevents viewing without the password; a “permissions password” restricts printing or editing but is weaker protection.

Electronic vs digital signature

An electronic signature can be a typed name or drawn image. A digital signature uses a cryptographic certificate to prove who signed and that the file was not changed. Some legal processes require qualified signatures from certified providers.

Bookmarks (outline)

The clickable table of contents shown in a viewer's sidebar.

Page size

A4 (210 × 297 mm) is standard in most countries; US Letter (8.5 × 11 in) in the US and Canada.

Linearised (“fast web view”)

A PDF arranged so the first page can display before the whole file downloads.

Which terms matter most day to day?

For everyday tasks: compression and DPI (file size), OCR (searchability), flattening (forms) and real redaction (privacy). Our guides on compressing and splitting put them into practice.