Heading structure is incorrect

Messages you may see

• Acrobat Accessibility Checker: Appropriate nesting - Failed (Appropriate nesting)
• PDF/UA-1 (ISO 14289-1) rule 7.4.2-1: For documents that are not strongly structured, as described in ISO 32000-1:2008, 14.8.4.3.5, heading tags shall be used as follows: (*) If any heading tags are used, H1 shall be the first. …
• PDF/UA-1 (ISO 14289-1) rule 7.4.4-1: Each node in the tag tree shall contain at most one child H tag
• PDF/UA-1 (ISO 14289-1) rules 7.4.4-2 and 7.4.4-3: All documents shall be either strongly or weakly structured, but not both
• PDF/UA-2 (ISO 14289-2) rule 8.2.5.12-1: Conforming files shall not use the H structure type
• Matterhorn Protocol 1.1, 14-002: Does use numbered headings, but the first heading tag is not H1.
• Matterhorn Protocol 1.1, 14-003: Numbered heading levels in descending sequence are skipped (Example: H3 follows directly after H1).
• Matterhorn Protocol 1.1, 14-006: A node contains more than one H tag.
• Matterhorn Protocol 1.1, 14-007: Document uses both H and H# tags.

What the rule requires

ISO 14289-1 (PDF/UA-1) distinguishes two ways of tagging headings. Weakly structured documents use numbered heading tags H1 to H6; this is what Word, InDesign and Acrobat produce. Strongly structured documents nest sections (Sect) and give each one a generic H heading, whose level follows from the nesting.

For weakly structured documents, clause 7.4.2 (rule 7.4.2-1) sets these conditions:

• If headings are used, the first one is H1.
• Going down the hierarchy, levels must follow in strict numerical order without skipping: H1 may be followed by H2, not by H3.
• A level may be repeated as often as the content needs, and the sequence may go back up to a higher level without restarting at H1.

For strongly structured documents, clause 7.4.4 requires that each node has at most one H child (rule 7.4.4-1). Rules 7.4.4-2 and 7.4.4-3 forbid mixing the two systems: a document uses either H or H1 to H6. PDF/UA-2 (ISO 14289-2) no longer allows the generic H at all (rule 8.2.5.12-1). The machine-checkable PDF/UA-2 rules contain no test for skipped levels; a logical heading hierarchy remains good practice and is expected under WCAG 1.3.1.

In the Matterhorn Protocol 1.1 these are failure conditions 14-002, 14-003, 14-006 and 14-007 of checkpoint 14 (Headings). Condition 14-001, “Headings are not tagged”, is a human check: text that looks like a heading but is tagged as P is invisible to a machine check. A document without any heading tags therefore passes rule 7.4.2-1.

Why it matters

Screen reader users often move through long documents by heading: they open a list of all headings or jump to the next heading of a given level. The heading levels tell them how the document is organised. If a level is skipped, they assume that content is missing; if the first heading is an H2 or H3, they cannot tell where the main title is.

Headings are also the basis for bookmarks generated from the structure and for the outline in reflow and export. WCAG success criterion 1.3.1 (Info and Relationships) and 2.4.6 (Headings and Labels) apply; the W3C technique PDF9 describes heading tags in PDF. Adobe notes that the order of headings is an advisory technique under WCAG, while PDF/UA-1 makes it a requirement.

Common causes

• In Word, heading styles were chosen by their look, for example Heading 3 because it is the right size, so a level is skipped.
• The cover title is not a heading, so the first tagged heading is H2.
• In InDesign, the Export Tagging of paragraph styles was left at Automatic. Adobe's help says this produces P tags without any heading structure, unless an older XML mapping exists.
• Automatic tagging in Acrobat guessed heading levels from font sizes.
• Documents were assembled from parts with different heading conventions, or a tool combined generic H tags with H1 to H6.

Example

Document
  H2   "Annual Report 2025"      <- first heading is not H1
  P    "..."
  H4   "Budget"                  <- H3 skipped
  P    "..."

Document
  H1   "Annual Report 2025"
  P    "..."
  H2   "Budget"
  H3   "Personnel costs"
  P    "..."
  H2   "Outlook"                 <- going back up is allowed
  P    "..."

Document
  Sect
    H    "Annual Report 2025"
    Sect
      H    "Budget"
      P    "..."

How to fix it

Microsoft Word

1. Format headings with the built-in styles Heading 1, Heading 2 and so on (Home tab, Styles gallery). Use Heading 1 for the main title or for chapter titles, and do not skip a level.
2. Change the look of a level by modifying the style, not by choosing a different level.
3. Do not imitate headings with bold or larger text; such text is exported as a normal paragraph.
4. Check the outline in the Navigation pane (View > Navigation Pane), then save as PDF with Document structure tags for accessibility checked.

Adobe InDesign

1. Open the paragraph style of each heading level (Paragraph Styles panel, Style Options) and select Export Tagging.
2. Under PDF, choose the tag H1, H2 and so on for the respective style. Map body text styles to P.
3. To map all styles at once, choose Edit All Export Tags in the Paragraph Styles panel menu and select PDF.
4. Export with Create Tagged PDF.

Adobe Acrobat Pro

1. In the Accessibility Checker panel, right-click Appropriate nesting and choose Show in Tags Panel.
2. To change a level, select the element in the Accessibility tags panel, choose Properties and change the type, for example from H3 to H2.
3. Alternatively, use All tools > Prepare for accessibility > Fix reading order, select the heading text and choose Heading 1 to Heading 6.
4. Run the check again, and check the file with our PDF accessibility checker to see rule 7.4.2-1 per heading.

Questions

May a document have several H1 headings?

Yes. PDF/UA-1 allows any level to be repeated. Several H1 are common, for example for chapter titles.

Can I go from H4 back to H2?

Yes. Only skipping levels on the way down is a failure. Going back up to a higher level is allowed.

What about more than six levels?

H7 and higher are not standard structure types in PDF 1.7 and have to be role-mapped to a standard type. Most documents are easier to navigate with fewer levels.

Sources

1. ISO 14289-1:2014 Document management applications – Electronic document file format enhancement for accessibility – Part 1: Use of ISO 32000-1 (PDF/UA-1) – International Organization for Standardization (ISO). Checked on 7 November 2026.
2. ISO 14289-2:2024 Document management applications – Electronic document file format enhancement for accessibility – Part 2: Use of ISO 32000-2 (PDF/UA-2) – International Organization for Standardization (ISO). Checked on 7 November 2026.
3. The Matterhorn Protocol 1.1 – PDF Association. Checked on 7 November 2026.
4. Matterhorn Protocol checks (list of checkpoints and failure conditions) – PDF Association (Tagged PDF School). Checked on 7 November 2026.
5. PDF9: Providing headings by marking content with heading tags in PDF documents – W3C Web Accessibility Initiative (WCAG 2.2 Techniques). Checked on 7 November 2026.
6. Create and verify PDF accessibility, Acrobat Pro – Adobe (Acrobat User Guide), 23 July 2025. Checked on 7 November 2026.
7. Reading Order tool for PDFs (Adobe Acrobat Pro) – Adobe (Acrobat User Guide), 9 May 2025. Checked on 7 November 2026.
8. Make your Word documents accessible to people with disabilities – Microsoft Support. Checked on 8 November 2026.
9. Creating accessible PDFs – Adobe (InDesign User Guide), 24 May 2023. Checked on 7 November 2026.
10. Map styles to export tags in InDesign – Adobe (InDesign User Guide), 2 June 2026. Checked on 7 November 2026.