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Table structure is invalid or header cells are not assigned

A data table in a PDF needs a fixed tag structure (Table, rows, header and data cells), the same number of cells in every row, and header cells that can be assigned to the data cells. Acrobat checks this with the rules Rows, TH and TD, Headers and Regularity; PDF/UA checkers with rules from clauses 7.2 and 7.5 of PDF/UA-1.

Updated

Messages you may see

  • Acrobat Accessibility Checker: Rows - Failed (TR must be a child of Table, THead, TBody, or TFoot)
  • Acrobat Accessibility Checker: TH and TD - Failed (TH and TD must be children of TR)
  • Acrobat Accessibility Checker: Headers - Failed (Tables should have headers)
  • Acrobat Accessibility Checker: Regularity - Failed (Tables must contain the same number of columns in each row and rows in each column)
  • PDF/UA-1 (ISO 14289-1) rule 7.2-3: Table element may contain only TR, THead, TBody, TFoot and Caption elements
  • PDF/UA-1 (ISO 14289-1) rule 7.2-10: TR element may contain only TH and TD elements
  • PDF/UA-1 (ISO 14289-1) rule 7.2-15: A table cell shall not have intersection with other cells
  • PDF/UA-1 (ISO 14289-1) rule 7.2-42: Table rows shall have the same number of columns (taking into account column spans)
  • PDF/UA-1 (ISO 14289-1) rule 7.5-1: If the table's structure is not determinable via Headers and IDs, then structure elements of type TH shall have a Scope attribute
  • PDF/UA-2 (ISO 14289-2) rule 8.2.5.26-1: Tables shall be regular. A table cell shall not have intersection with other cells
  • PDF/UA-2 (ISO 14289-2) rule 8.2.5.26-5: When a table contains header cells, that table shall provide sufficient semantic information to allow accurate determination of which of its table header cells (structure element TH) pertain to other cells as specified in ISO 32000-2:2020, 14.8.5.7
  • Matterhorn Protocol 1.1, 15-003: In a table not organized with Headers attributes and IDs, a TH cell does not contain a Scope attribute.
  • Matterhorn Protocol 1.1, 09-004: A table-related structure element is used in a way that does not conform to the syntax defined in ISO 32000-1, Table 337.

What the rule requires

The machine-checkable table rules of PDF/UA-1 (ISO 14289-1) fall into three groups:

  • Nesting (rules 7.2-3 to 7.2-14, 7.2-16 and 7.2-36 to 7.2-39): a Table contains only TR, THead, TBody, TFoot and at most one Caption as first or last child. THead, TBody and TFoot contain only TR; a TR contains only TH and TD. A table has at most one THead and one TFoot, and if it has either, it also needs a TBody.
  • Regularity (rules 7.2-15, 7.2-41 to 7.2-43): cells must not overlap, and taking RowSpan and ColSpan into account, every row has the same number of columns and every column the same number of rows.
  • Header assignment (clause 7.5, rules 7.5-1 and 7.5-2): each data cell's headers must be determinable. If the table does not use Headers and ID attributes, every TH needs a Scope attribute (Row, Column or Both).

PDF/UA-2 (ISO 14289-2) bundles the same requirements in rule 8.2.5.26: tables must be regular (8.2.5.26-1 to -4), and header cells must be assignable to the cells they describe (8.2.5.26-5 and -6).

The Matterhorn Protocol 1.1 lists table syntax as failure condition 09-004 (checkpoint 09, Appropriate tags) and a TH without Scope as 15-003 (checkpoint 15, Tables). Our report follows this split: syntax findings appear under checkpoint 09, missing Scope under checkpoint 15. Human checks include 15-001 and 15-002 (a header cell is not tagged as header), 15-004 (a layout grid is tagged as a table) and 15-005 (a cell's header cannot be determined unambiguously). The protocol also notes that irregular tables are “almost always a strong indicator of improper table structure”.

Why it matters

Screen readers announce a table with its number of rows and columns and let users move cell by cell. On each move they read the relevant row and column headers, for example “2025, North, 1,040”. If header cells are tagged as TD, or a row has fewer cells than the others, the counts are wrong and headers are assigned to the wrong cells, so numbers are read without context or with the wrong context.

Cells that sit outside a row may be read separately after the table or not at all. Reflow and export to other formats also depend on a valid table structure. WCAG success criterion 1.3.1 (Info and Relationships) applies; the W3C technique PDF6 shows correct table tags.

Common causes

  • In Word, the header row is not marked, cells are merged or split, or empty rows and columns were used for spacing. Microsoft advises against merged and split cells and nested tables.
  • Tables were built with tabs or spaces instead of table functions, so there is no table structure at all, or a layout grid was tagged as a data table.
  • Automatic tagging in Acrobat misread a table without clear borders. Adobe's help notes that tables without well-defined borders and rules are often tagged incorrectly.
  • A table that runs across pages was exported as two tables, with the repeated header row tagged as data.
  • A tool or a manual correction placed TD directly under Table or put text between rows.
  • Header cells exist but have no Scope, and the table has no Headers/ID associations.

Example

Table
  TR
    TD  "District"          <- header tagged as data
    TD  "2024"
    TD  "2025"
  TD  "North"               <- TD directly under Table
  TR
    TD  "South"
    TD  "1,120"             <- 2 cells, other rows have 3
Failing: header text tagged as TD, a TD outside a row, an incomplete row
Table
  THead
    TR
      TH  "District"   Scope=Column
      TH  "2024"       Scope=Column
      TH  "2025"       Scope=Column
  TBody
    TR
      TH  "North"      Scope=Row
      TD  "980"
      TD  "1,040"
    TR
      TH  "South"      Scope=Row
      TD  "1,050"
      TD  "1,120"
Fixed: THead and TBody, TH with Scope, regular rows
52 0 obj
<< /Type /StructElem /S /TH /P 51 0 R
   /A << /O /Table /Scope /Column >>
   /Pg 8 0 R /K 12 >>
endobj
Scope as a table attribute on a TH structure element

How to fix it

Microsoft Word

  1. Use a real table (Insert > Table) for tabular data, not tabs or spaces, and do not use tables for page layout.
  2. Mark the first row as header: Table Design tab, Table Style Options group, Header Row.
  3. Also select the header row, right-click, choose Table Properties and on the Row tab check Repeat as header row at the top of each page (or choose Repeat Header Rows on the Table Layout tab). Word exports rows set this way as header cells.
  4. Avoid merged and split cells, nested tables and blank rows or columns; Review > Check Accessibility reports many of these problems.
  5. Save as PDF with Document structure tags for accessibility checked. Word has no setting for Scope; if rule 7.5-1 is reported afterwards, set it in Acrobat.

Adobe InDesign

  1. Create tables with InDesign's table functions (for example Table > Convert Text to Table), not with tabs.
  2. Select the header row with the Type tool and choose Table > Convert Rows > To Header. InDesign exports header rows as header cells in a tagged PDF.
  3. Keep tables regular: avoid merged cells where a simple grid is possible.
  4. Export with Create Tagged PDF and check the table in Acrobat; set Scope there if rule 7.5-1 is reported.

Adobe Acrobat Pro

  1. Open the Reading Order tool with All tools > Prepare for accessibility > Fix reading order. If the table is not recognised, drag a selection around it and choose Table.
  2. Select the table and choose Table Editor. The cells are outlined with their tags.
  3. Right-click each header cell and choose Table Cell Properties. Change Data Cell to Header Cell and set Scope to Column or Row. For merged cells, set Row Span or Column Span to the number of cells covered.
  4. For complex tables, give header cells an ID and list the matching header IDs on each data cell (Associated Header Cell IDs in the same dialog).
  5. Fix nesting errors in the Accessibility tags panel: drag elements so that Table contains THead/TBody/TFoot or TR, and every TR contains only TH and TD. In the Accessibility Checker, Show in Tags Panel jumps to the failed element.

Check your PDF

Upload the fixed file to see which machine-checkable criteria it meets now. The report lists the remaining problems with their pages.

Open the checker

Questions

Do layout tables have to follow these rules?
Content that only arranges text visually should not be tagged as a table at all (Matterhorn 15-004). Tag it as paragraphs, lists or sections instead.
Is a table summary required?
No. Acrobat checks for a summary, but Adobe's help calls table summaries optional. PDF/UA-1 does not require one.

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. PDF6: Using table elements for table markup in PDF Documents – W3C Web Accessibility Initiative (WCAG 2.2 Techniques). Checked on 7 November 2026.
  6. PDF20: Using Adobe Acrobat Pro's Table Editor to repair mistagged tables – W3C Web Accessibility Initiative (WCAG 2.2 Techniques). Checked on 7 November 2026.
  7. Create and verify PDF accessibility, Acrobat Pro – Adobe (Acrobat User Guide), 23 July 2025. Checked on 7 November 2026.
  8. Reading Order tool for PDFs (Adobe Acrobat Pro) – Adobe (Acrobat User Guide), 9 May 2025. Checked on 7 November 2026.
  9. 2.11 Formatting Tables in Acrobat (TCEQ Adobe Acrobat Accessibility Guide) – Texas Commission on Environmental Quality. Checked on 7 November 2026.
  10. Make your Word documents accessible to people with disabilities – Microsoft Support. Checked on 8 November 2026.
  11. Repeat table header on subsequent pages – Microsoft Support. Checked on 8 November 2026.
  12. Creating accessible PDFs – Adobe (InDesign User Guide), 24 May 2023. Checked on 7 November 2026.