The tag tree is the backbone of an accessible PDF. Without it, a screen reader sees your document as a flat stream of text and images — no headings to jump between, no lists, no table structure. Understanding tags is the foundation of understanding PDF accessibility.
What the tag tree is
Tags are hidden structural labels embedded in the PDF. They tell assistive technology what each piece of content is — a heading, a paragraph, a list item, a table cell, a figure. Together they form a hierarchy called the tag tree, which mirrors how the document should be read and navigated. A well-tagged PDF lets a screen reader user skip to headings, understand lists as lists, and hear tables read in a sensible order. This is the core of PDF/UA.
The common tag types
- H1–H6 — headings, defining the document outline
- P — paragraph text
- L, LI — lists and list items
- Table, TH, TD — tables, header cells, and data cells
- Figure — images (with alternative text)
- Link — hyperlinks (with meaningful text)
Tagged vs untagged: what a screen reader sees
An untagged PDF is essentially a picture of a document. A screen reader reads it left-to-right, top-to-bottom across the whole page — including across multi-column layouts, so columns get jumbled together. There are no headings to navigate by. A tagged PDF reads in logical order, announces structure ("heading level 2," "list, 4 items"), and lets users jump around. The difference is night and day. Scanned PDFs are the worst case — they're images with no text at all until OCR'd and re-tagged.
How to view the tag tree
In Adobe Acrobat Pro, open View → Show/Hide → Navigation Panes → Tags. You'll see the tree expand from the document root. This is where manual remediation happens — dragging content into the right tags, fixing order, adding missing structure.
How tags get built
Some applications export tagged PDFs from accessible source documents (a Word file with real heading styles, properly alt-tagged images, and real table headers exports to a reasonably tagged PDF). When the source isn't accessible, or the PDF was scanned, the tags must be added — either manually in Acrobat or via automated remediation that rebuilds the tree programmatically and validates it with veraPDF.
Check your tags
Run your PDF through the free checker. The report tells you immediately whether the document is tagged and where the structure breaks. See how to read the report and the six failures that break screen readers.