TH has associated cells

TH has associated cells is a PDF/UA table check in PAC, the free PDF Accessibility Checker. It fails when PAC can't work out which data cells a header cell (a TH tag in the table's hidden structure) describes. In a simple table, that link comes from the header cell's scope: Column, Row or Both. In a complex table, each data cell lists the IDs of its headers. Without one of these, a screen reader can't tell which header belongs to which value.

What this means

Screen readers read tables one cell at a time. When someone moves to a new cell, the screen reader announces the header for that row or column, so "$1.2 million" becomes "Fiscal year 2027, Parks: $1.2 million". That only works when each header cell is tied to its data cells:

• Scope on a TH says whether it labels the cells below it (Column), the cells to its right (Row), or both.
• Headers and IDs are for tables a single scope can't describe, such as tables with two levels of column headers. Each header cell gets an ID, and each data cell lists the IDs of the headers that apply to it.

PDF/UA, the ISO standard for accessible PDFs, requires one of these methods for every header cell, and PAC shows the check among its table results ("PDF/UA table"). Common reasons it fails:

• Header cells are tagged TH, but no scope was ever set.
• The scope points the wrong way, such as Row on a column header.
• Empty cells were left untagged, so a row header has no data cells in its row to point to.
• A title or note row inside the table is tagged as a header, even though it doesn't label any column.

Why it matters

Without these links, a screen reader user hears a run of numbers with no labels, or with the wrong labels. In a budget, a fee schedule or a meeting calendar, that can mean reading a value under the wrong department or date. This is a failure of WCAG 2.1 success criterion 1.3.1, Info and Relationships, because the table's structure is visible but not available to assistive technology.

How to fix it in Acrobat Pro and re-check in PAC

Fix it in the source file

Simple tables in the source export more reliably than complex ones fixed in Acrobat.

• Word: put column headers in the first row, then select that row and turn on Repeat as header row at the top of each page (Table Properties > Row). Avoid merged cells and blank rows used for spacing. Microsoft's documentation shows Word exporting header cells as TH but doesn't mention scope, so check each export in PAC. If this error appears, set the scope in Acrobat or let a fix tool do it.
• InDesign: turn the top rows into real header rows with Table > Convert Rows > To Header.
• Any app: keep tables simple, with one header row and at most one header column. Split very complex tables into smaller ones where you can.

Fix it automatically with Includoc

Includoc sets the scope of every header cell automatically. Deciding which cells are headers takes judgment, so our AI identifies header rows and columns and you confirm them in the tables panel on the review screen.

Simple tables are fixed end to end. Complex tables, such as those with merged cells or several levels of headers, are flagged for review with suggested headers. If a complex table matters, such as a budget people rely on, the human-verified tier checks it for you.

Standards

Related errors

• Table rows, TH and TD, Headers and Regularity – Failed: Acrobat's table rules, including tables with no header cells at all.
• Content is tagged or artifacted: table borders and shading often trigger this check too.

For a full walkthrough, read Tables in PDFs, or check a PDF free to see which tables need work.