PDF Tagging

The process of adding a logical structure tree to a PDF so that assistive technologies can interpret the document's content, reading order, and semantics independently of its visual layout. Tags label each piece of content with its role — heading, paragraph, list item, figure, table, form field — and can carry alt text, language, and other metadata. A properly tagged PDF is the core requirement of the PDF/UA accessibility standard and of most regional mandates (Section 508, EN 301 549). Untagged or incorrectly tagged PDFs are a dominant source of accessibility failures: studies have found fewer than 3% of PDFs on the web are adequately tagged.