Why does a PDF contain different errors after improvement than in the original check?

Different results after improvement

It may happen that a PDF displays new or different errors after improvement than before.

Cause: missing markup in the original

The reason for this is usually that the original document was not tagged.

Untagged PDF: Elements such as headings, paragraphs or tables are not marked as such.
After improvement: The PDF is tagged – structures and content are marked correctly.

Result of the tagging structure

This new structure allows the checking tool to detect additional or different errors that were not visible in the original document.
The errors therefore only appear once the content has been tagged.