PAC Errors Explained: What Each PDF Accessibility Failure Actually Means

PAC (PDF Accessibility Checker) is one of the fastest ways to spot PDF accessibility issues — but the messages can feel cryptic, especially when you’re looking at dozens (or hundreds) of files.

This guide translates common PAC findings into plain English, explains what typically causes them, and lists the first places to look when you need a fix. It’s written for university and public-sector teams who need consistent results at scale.

How to read PAC results (the practical way)

Think of PAC results in three buckets:

• Structure: tags, headings, lists, tables, reading order
• Alternatives: alt text, artifacting, language, metadata
• Usability: forms, interactive elements, logical navigation

1) “Document is not tagged” / missing tag structure

What it means: Screen readers rely on tags. If the PDF has no tag tree, it’s essentially unstructured.

Common causes:

• Exported without “Document structure tags for accessibility” enabled
• Printed-to-PDF instead of exported
• Scanned PDF with no tagging workflow

First places to check:

• Export settings in Word/Office
• Acrobat: Tags panel — is there a tag tree?
• Is a better source file available?

2) “Path object not tagged”

What it means: A vector “path” exists on the page (often a shape or decorative element) but PAC sees it as content without tags.

Common causes:

• Decorative shapes or lines exported as page content
• Artifacts not properly marked as artifacts
• Background design elements that became “real” objects in the PDF

First places to check:

• In the source document: remove unnecessary shapes, or ensure they’re decorative
• In Acrobat: mark decorative objects as artifacts
• Verify no invisible “floating” shape objects are overlapping text

3) “Invalid use of a ‘Span’ structure element”

What it means: A <Span> tag is being used where a more appropriate structure is required, or the tag tree is malformed.

Common causes:

• Export created unusual tag nesting
• Manual tag edits introduced invalid structure
• Text boxes, grouped objects, or complex layout caused tag fragmentation

First places to check:

• Re-export from a cleaned-up source document
• In Acrobat: inspect the tag tree around the reported location
• Simplify layout: reduce floating text boxes and overlapping elements

4) “Alternative text missing” (figures/images)

What it means: A figure is present and tagged as content, but has no alt text.

Common causes: missing alt text in the source, or a decorative image that should be artifacted instead.

First places to check:

• In Word: right-click image → Alt Text
• In Acrobat: set alt text on the Figure tag, or mark as artifact if decorative

5) “Title missing” / metadata issues

What it means: The PDF lacks key metadata used by assistive tech and user agents.

Common causes: exported without document properties set; title not configured to display.

First places to check:

• Acrobat: File → Properties → Description (Title, Author)
• Acrobat: Initial View → “Show: Document Title”

6) “Language missing”

What it means: Screen readers need a document language to choose correct pronunciation rules.

Fix: set document language in Acrobat, and ensure language changes are tagged if necessary.

7) Forms issues (missing tooltips, fields not labeled)

What it means: Form fields aren’t properly labeled for assistive technology.

First places to check:

• Acrobat: field properties → Tooltip (often becomes the accessible name)
• Tab order and reading order around the form
• If possible, rebuild forms from accessible templates

Common troubleshooting sequence (fastest to slowest)

1. Confirm tagging exists (if not, re-export from source)
2. Clean up the source layout (remove floats/text boxes where possible)
3. Re-export and retest (often solves “invalid structure” problems)
4. Only then perform manual tag surgery in Acrobat

Bottom line

PAC is most powerful when you treat it as a diagnostic tool inside a repeatable workflow. Translate the message → fix at the source when possible → re-export → validate again → manual QA for key documents. That’s how you keep quality high without spending hours per file.