Your PDF failed the accessibility check. Here's what the error means.
PAC, veraPDF and Acrobat all hand back the same kind of list: a column of red items with terse names. Most of those names describe a handful of underlying problems, and most of those are mechanical enough to repair automatically.
Below are the ones people search for most: what each one actually means, and whether a tool can fix it or a person has to decide.
"Path object not tagged" / "Text object not tagged"
Something is drawn on the page that the structure tree doesn't account for. Every mark in a PDF/UA file has to be one of two things: real content that carries a tag, or decoration explicitly marked as an artifact. A stray table rule, a logo, a page border, a text run skipped during export — any of them can be left dangling.
Fixable automatically. The work is deciding which of the two each object is, then tagging or artifacting it.
"Alternative description missing"
An image, a figure or a link annotation carries no alt text, so a screen reader reaching it announces nothing useful.
Fixable, with a caveat. Generating alt text is automatic; whether the description is right for your context is a judgment call. Our reports mark generated descriptions, so you can review the ones that matter.
"Natural language cannot be determined"
The document, or a passage inside it, doesn't declare what language it's in. Screen readers then read it in the wrong voice — a Hungarian paragraph through an English synthesizer is noise.
Fixable automatically, including per-passage language switches in mixed-language documents.
"Document title is not set" / DisplayDocTitle
The PDF has no title in its metadata, or the viewer is told to show the filename instead of
the title. This is why some documents open in Acrobat as final_v3_REALLY_final.pdf.
Fixable automatically.
"Font not embedded"
The file references a font that isn't inside it. Text may render with a substitute, and extraction — the thing assistive technology depends on — can break.
Fixable in most cases by embedding or repairing the font. Where the original outlines are genuinely gone, no tool can invent them.
"Numbered heading skips one or more heading levels"
The document jumps from H1 to H3. Screen reader users navigate by heading level, so a gap breaks the outline they rely on.
Fixable automatically where the visual hierarchy makes the intent clear.
"Link annotation is not nested inside a Link structure element"
A clickable region exists on the page but sits outside the tag structure, so it never reaches the accessibility tree.
Fixable automatically.
"Artifact present inside tagged content"
Decoration ended up inside a tagged block, or real content got marked as decoration. The second case is worse: that content disappears from the reading order entirely.
Fixable automatically.
"Irregular table"
A cell is missing, or the row and column spans don't add up. Visually the table looks fine while its semantics are broken, and a screen reader announces the wrong header for a cell.
Partly fixable. Regular grids repair cleanly. Genuinely irregular layout tables often need a person to say what the structure was meant to be.
"Figure element with no bounding box"
A figure on a single page carries no /BBox, so its extent is undefined.
Fixable automatically.
What can't be checked by any tool
The Matterhorn Protocol breaks PDF/UA conformance into roughly 136 failure conditions. About two-thirds are machine-checkable, and the errors above are all in that group. The rest need human judgment: whether alt text is meaningful, whether the reading order is logical for a given layout, whether a table's headers say what the author intended.
No tool can honestly certify those automatically. Ours flags them with their page location instead of pretending they're covered.
What a11yfy does with the list
Upload the file and the analysis is free: you get the same checkpoint-level breakdown your validator just gave you, with each item marked as automatically repairable or needing review, and the estimated credit cost before you spend anything.
Run the repair and you get back a tagged PDF/UA-1 file, validated with veraPDF, plus a report you can hand to whoever asked for proof.
Upload your PDF — the analysis is free, and you see the price before you commit. Prefer the standard first? Read what PDF/UA requires.