This glossary explains 30+ PDF-related terms in plain language. Each entry is a short definition followed by a longer paragraph with practical context — formats, operations, security, archival standards, and underlying technology. Updated May 2026.
PDF — Portable Document Format, an ISO 32000 open standard since 2008. PDF/A — archival variant (ISO 19005) banning JavaScript, encryption, and external font references; required by government archives, courts, libraries. PDF/X — prepress variant (ISO 15930) for commercial printing with strict color and font requirements. PDF/UA — Universal Accessibility (ISO 14289), required by Section 508 and the EU Web Accessibility Directive. PDF/E — Engineering variant (ISO 24517) for 3D models and CAD data. Tagged PDF — adds a logical structure tree alongside visual content, required for screen reader accessibility and reliable text reflow.
Compression — reduces file size by image downsampling, codec re-encoding (JPEG 2000, JBIG2), Flate/Deflate streams, and font deduplication. OCR — Optical Character Recognition converts pixel-based scanned text into searchable, selectable text. Redaction — permanent removal of sensitive content (not just visual blackout). Flattening — merges form fields, annotations, and layers into static page content. Bates numbering — sequential page numbering with prefix for legal/medical document sets.
Encryption — password protection via RC4 (legacy) or AES-256 (modern). Digital signature — cryptographic binding of identity to document via X.509 certificates, legally recognized under eIDAS (EU) and ESIGN (US). Metadata — hidden data in PDFs (author, software, GPS, edit history) that frequently leaks confidential information; clean with Clean Metadata.
WebAssembly (Wasm) — browser-native bytecode enabling near-native PDF processing without server uploads. JBIG2 — compression for monochrome scans (5-10× more efficient than older codecs; carries a famous Xerox character-swap pitfall in lossy mode). PDF.js — Mozilla's open-source JavaScript PDF rendering engine. pdf-lib — open-source library for creating and modifying PDFs entirely in the browser.
Now apply what you learned — explore all 46 PDF tools: compress, OCR, redact, sign, encrypt, convert to PDF/A, and more. All free, all in your browser.