PDF tagging is the structural backbone of an accessible PDF. A tagged PDF contains hidden metadata describing what every element on the page is — which text is a heading, which is a paragraph, which image needs a description, how tables are structured, what order content should be read in. Without tags, a PDF is just a visual layout with no machine-readable structure.
What PDF Tags Are
Tags in a PDF work similarly to HTML tags on a web page. Just as HTML uses <h1> for headings and <p> for paragraphs, PDF tags mark each content element with its type and role. The tag tree — a hierarchical structure embedded in the PDF — describes the document's logical organization:
- <H1>, <H2>, <H3>: heading elements at different levels, enabling navigation by heading
- <P>: paragraph text, the most common content element
- <Figure>: images and graphics, which can carry alternative text descriptions for screen readers
- <Table>, <TR>, <TD>: table structures with rows and cells, enabling screen readers to announce column and row headers
- <L>, <LI>: list and list item elements, so screen readers announce "list of 5 items" before reading each entry
Why Tagging Matters
Tags are what make a PDF accessible to people using assistive technology. A screen reader processing an untagged PDF has no way to distinguish a heading from body text, can't identify which text is a table cell header, and doesn't know which images need to be described versus which are purely decorative. The reading experience becomes confusing or impossible.
Beyond PDF Accessibility, tags benefit everyone. Tags enable reliable text reflow on small screens — a tagged PDF can reflow content to fit a phone display. Tags make copy-paste more reliable by providing reading order information. Tags enable better search indexing by document management systems. And tags are required for legal compliance with accessibility standards including Section 508 in the US and EN 301 549 in Europe.
How to Check If a PDF Is Tagged
In Adobe Reader or Acrobat, check File > Properties > Description tab. Look for "Tagged PDF: Yes" or "Tagged PDF: No." A quick functional test: enable Read Out Loud (View > Read Out Loud > Activate Read Out Loud) and listen to how the document is announced. A well-tagged PDF reads logically; an untagged or poorly tagged PDF either fails to read at all or reads content in a confusing order.
Acrobat Pro's Accessibility Checker (Tools > Accessibility > Full Check) provides a detailed report identifying specific tagging issues — missing alternative text on images, incorrect heading hierarchy, tables without header tags, and other problems that affect PDF Accessibility compliance.
How PDFs Get Tagged
The best way to get a tagged PDF is to export from a well-structured source document. Microsoft Word documents using proper Heading styles, list formatting, and structured tables export with tags automatically when using File > Save As > PDF. The tag structure mirrors the document's heading hierarchy and content organization.
Google Docs also exports tagged PDFs when downloaded as PDF. InDesign requires explicit accessibility settings during export to generate tags. The key in all cases is using semantic structure — proper heading styles rather than manually bolded text, list formatting rather than manually indented lines — which the export engine can map to PDF tags.
Adding Tags to an Existing Untagged PDF
Acrobat Pro can add tags to an existing untagged PDF automatically: Tools > Accessibility > Add Tags to Document. The auto-tagging analyzes the page layout and attempts to infer heading levels, paragraphs, and list structure from the visual formatting. For simple documents, auto-tagging works well. For complex layouts, it produces a starting point that needs manual review and correction.
Manual tag editing in Acrobat Pro is done through the Tags panel (View > Show/Hide > Navigation Panes > Tags). The panel shows the full tag tree and lets you add, delete, move, and retype tags. This is detailed work — a thorough remediation of a complex untagged PDF can take hours — but it's the only path to full accessibility compliance when the source document isn't available.
When Tagging Is Required
Government agencies, public sector organizations, educational institutions, and any organization receiving federal funding in the US are typically required to produce accessible PDFs under Section 508. Legal documents filed electronically with courts that mandate accessibility compliance must be tagged. Corporate organizations increasingly require accessible PDFs for HR documents, policies, and external publications as part of broader PDF Standard compliance and ESG commitments. If your organization distributes PDFs to the public, tagging is increasingly expected — not just best practice.