PDF Accessibility Glossary
Plain-language definitions of the key PDF accessibility terms — PDF/UA, WCAG, tags, alt text, reading order, Section 508, and more.
- ADA (Americans with Disabilities Act)
- US civil-rights law that prohibits discrimination against people with disabilities. Courts increasingly treat PDFs on public-facing websites as covered by the ADA, so inaccessible documents can create legal exposure. Learn more
- Alternative text (alt text)
- A short text description a screen reader announces in place of an image, conveying the same information to people who cannot see it. Meaningful images need alt text; purely decorative images should be marked as artifacts instead. Learn more
- Artifact
- A piece of content marked as decorative so assistive technology skips it — for example a background flourish, divider, or running header. Artifacting decorative items is as important as adding alt text to meaningful ones. Learn more
- Assistive technology
- Software or hardware people with disabilities use to access content, such as screen readers, screen magnifiers, and switch or voice input. An accessible PDF exposes its structure so these tools can interpret it correctly.
- Color contrast
- The luminance difference between text and its background. WCAG requires at least 4.5:1 for body text (3:1 for large text) so low-vision readers can read it, and color must not be the only way information is conveyed. Learn more
- Document title
- A meaningful title stored in the PDF’s metadata and set to display in place of the file name. It helps all users — especially screen reader users — tell documents apart. Required by WCAG 2.4.2 Page Titled. Learn more
- European Accessibility Act (EAA)
- EU directive requiring many products and services — including digital documents — to be accessible. It references WCAG 2.x Level AA, the same technical target used by most other accessibility regimes. Learn more
- Form fields
- Interactive controls in a PDF such as text inputs, checkboxes, and dropdowns. Each needs an accessible name (tooltip), clear instructions, and a logical tab order so it can be completed with a keyboard and screen reader. Learn more
- Heading structure
- The outline created by headings tagged H1–H6. Screen reader users navigate by it, so a document should use a single top-level heading and never skip levels (jumping H2 straight to H4 is a failure). Learn more
- Language (document language)
- The primary language declared in a PDF’s metadata, plus any passages marked in another language. It tells a screen reader which pronunciation rules to use. Required by WCAG 3.1.1 Language of Page. Learn more
- Link text
- The visible, accessible text of a hyperlink. It should describe the destination ("View the 2025 report") rather than say "click here", so the link makes sense out of context. Required by WCAG 2.4.4 Link Purpose. Learn more
- Matterhorn Protocol
- A set of 31 checkpoints broken into 136 failure conditions, created by the PDF Association to make the PDF/UA standard testable. Accessibility checkers map their tests to these checkpoints. Learn more
- OCR (Optical Character Recognition)
- Technology that converts the picture of text in a scanned, image-only PDF into real, selectable text that can be tagged and read by assistive technology. The first step in fixing a scanned document. Learn more
- PDF/UA (ISO 14289)
- The international standard that defines what makes a PDF accessible to assistive technology. It specifies the PDF-specific mechanics — complete tagging, reading order, alt text, table structure, language, and a conformance flag — that satisfy WCAG within the PDF format. Learn more
- Reading order
- The sequence in which a screen reader announces tagged content. It must match the logical reading order a person would follow; multi-column layouts, sidebars, and captions often end up out of sequence even when the page looks correct. Learn more
- Remediation
- The process of fixing an existing PDF’s accessibility problems — adding tags, alt text, reading order, table headers, and metadata — either manually or with automated tools, so the document meets PDF/UA and WCAG. Learn more
- Screen reader
- Software that reads on-screen content aloud or sends it to a braille display, used by people who are blind or have low vision. Common screen readers include NVDA and JAWS on Windows and VoiceOver on Apple devices.
- Section 508
- A US law requiring electronic content from federal agencies — and their contractors and grantees — to be accessible. Since the 2017 refresh its technical requirements align with WCAG 2.0 Level AA. Learn more
- Table headers
- Cells tagged as header cells (TH) with the correct scope so a screen reader can announce which row and column each data value belongs to. Layout tables used only for positioning should not be tagged as tables at all. Learn more
- Tagged PDF
- A PDF that carries a structure tree (tags) describing its content and reading order, which a screen reader can interpret. An untagged PDF has no such structure and is effectively unreadable to assistive technology. Learn more
- WCAG 2.1 AA
- The Web Content Accessibility Guidelines, version 2.1, Level AA — the technology-neutral standard most accessibility laws reference. For PDFs, a relevant subset of its success criteria applies, covering alt text, structure, contrast, titles, links, and language. Learn more
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