Common PAC and veraPDF errors and how to fix them

How to read the error list

The Matterhorn Protocol breaks the PDF/UA-1 requirements down into checkpoints covering metadata, fonts, headings, tables and more. PAC groups its results by these areas, while veraPDF names the relevant clause of the standard. Many individual messages often share a single cause: if the structure tree is missing entirely, the validator reports every single text object. Fix the fundamental errors first, then check again.

For each error we note whether EasyPDFUA detects it and whether it can be fixed automatically when you tag the PDF retroactively.

Metadata and document settings

Document title missing or not displayed

Cause: The XMP metadata has no dc:title, or DisplayDocTitle is not set to true in the viewer preferences. Screen readers then announce the file name instead of a meaningful title.
Fix: Enter a title in the document properties and enable “show document title”.
EasyPDFUA: detects and fixes both.

Default language missing

Cause: The document catalog has no /Lang entry. Screen readers fall back to their own default language and mispronounce the text.
Fix: Set the main language, for example en-GB or de-AT. Passages in other languages also need their own language attribute on the relevant tag.
EasyPDFUA: detects and sets the default language. Language changes within the text must be marked manually.

PDF/UA identifier missing

Cause: The XMP metadata contains no pdfuaid:part entry, so validators do not treat the file as a PDF/UA document.
Fix: Enable the PDF/UA option on export, or add the identifier afterwards, but only once the other requirements are met.
EasyPDFUA: adds the identifier when tagging.

Tagged content and artifacts

Document is not tagged

Cause: There is no structure tree (StructTreeRoot) and no MarkInfo flag. This often happens when printing to a PDF printer or exporting without the accessibility option.
Fix: Ideally, export again from the source file with tagging enabled. If the source is no longer available, retroactive tagging helps.
EasyPDFUA: detects the problem and creates a baseline structure tree with a document tag and one paragraph per page. This removes the fundamental errors but does not replace a semantic structure.

Content neither tagged nor marked as an artifact

Cause: Individual text, image or path objects are not assigned to any tag. This often affects stamps, headers or graphics added later.
Fix: Add meaningful content to the structure and mark purely decorative elements as artifacts.
EasyPDFUA: detects untagged content. When tagging, page content is assigned to the baseline structure; distinguishing content from decoration requires a manual review.

Artifact inside tagged content, or the other way round

Cause: Artifact and content markings are nested inside each other, usually after faulty post-processing.
Fix: Resolve the nesting in the content panel of an editing tool such as Acrobat Pro or axesPDF.
EasyPDFUA: does not fix this automatically. Documents that are already tagged are not restructured and are left unchanged if in doubt.

Fonts

Font not embedded

Cause: The PDF references a font without including it, so rendering depends on the reader’s system.
Fix: Export again with embedded fonts; this is usually a setting in the PDF export options.
EasyPDFUA: detects missing embedding but does not embed fonts afterwards.

Missing Unicode mapping (ToUnicode)

Cause: A font lacks the mapping from character codes to Unicode. Screen readers read out gibberish, and search and copy do not work.
Fix: Export again with a complete font or add the mapping.
EasyPDFUA: detects missing mappings and repairs them when they can be derived unambiguously from the embedded font.

Links, annotations and tab order

Link annotation not nested in a Link tag

Cause: A clickable area is not connected to the structure through a Link tag, or it has no description (Contents or alternative text).
Fix: Create a Link tag with an object reference for each link annotation and give it a meaningful description.
EasyPDFUA: detects and fixes this: link annotations receive a Link tag with a description.

Tab order does not follow the structure

Cause: Pages with annotations have no /Tabs /S entry, so keyboard navigation jumps through links and form fields in a different order.
Fix: Set the tab order to “use document structure”.
EasyPDFUA: sets the entry when tagging.

Semantic structure

Figure without alternative text

Cause: A Figure tag has no Alt attribute.
Fix: Add alternative text that describes the purpose of the image, or mark decorative images as artifacts.
EasyPDFUA: does not create figure tags or alternative text. These can only be assigned meaningfully with an understanding of the content.

Skipped heading level

Cause: An H1 is followed directly by an H3, or headings are only formatted visually and not tagged.
Fix: Use heading styles in the source file and build a complete hierarchy.
EasyPDFUA: does not create heading tags; this is manual work, ideally in the source.

Table without header cells

Cause: Tables consist only of TD cells, or header cells (TH) have no Scope. Screen readers cannot relate values to their column.
Fix: Mark header rows as such, for example with “repeat as header row” in Word, and define the scope.
EasyPDFUA: does not create table tags. Tables and lists must be tagged manually or when exporting from the source.

Recommended order

1. Examine the PDF with the PDF/UA check.
2. Add the basics such as title, language, identifier, baseline tags and links automatically with EasyPDFUA.
3. Check again with PAC or veraPDF.
4. Work on headings, tables, lists and alternative text manually, or export accessibly from the source.

Frequently asked questions

Why does PAC report thousands of errors?

Usually the basic structure is missing. If a PDF is not tagged, every single text object counts as an error. Once a structure tree exists, the number usually drops considerably.

What is the difference between PAC and veraPDF?

PAC is a free Windows application with a graphical interface and a screen reader preview. veraPDF is an open-source validator that works well on the command line and in automated workflows. Both check the machine-verifiable criteria of PDF/UA.

Can EasyPDFUA fix all PAC errors?

No. EasyPDFUA fixes technically unambiguous errors such as a missing title, missing language, PDF/UA identifier, baseline tags, link tags, tab order and Unicode mappings that can be repaired unambiguously. Headings, tables, lists and alternative text require manual work.

Does “no errors in PAC” mean the PDF is accessible?

Not necessarily. PAC only checks criteria a machine can decide. Whether alternative text is meaningful, headings are correct and the reading order is logical has to be judged by a person.