What this test checks
This test checks whether the PDF document is encrypted.
Why this maybe a barrier
When a PDF document is encrypted, even trivially with an empty password, it makes it very difficult for assistive technologies and PDF readers to open and process its contents.
Even when the password is provided, automated software such as assistive technology enabled screen readers may find it difficult to process the content. Encrypted PDF documents are hence a significantly high barrier to accessibility.
How this differs from Document Permissions check?
Encrypted document check is done right in the beginning of loading of the document and if encrypted, it is an immediate critical failure. None of the other checks are carried out if a PDF document is found encrypted. The accessibility score for an encrypted PDF document is zero.
When compared to this, a document permissions failure is less severe, since it doesn't cause a critical failure, though it is an accessibility barrier.
WCAG 2.2 Success Criterion
N.A (PDF/UA-only check)
PDF/UA Principle
Section 7.16: Security — This section lists down the security settings required to enable PDF documents for accessibility.
"An encrypted conforming file shall contain a P key in its encryption dictionary (ISO 32000-1:2008,
7.6.3.2, Table 21). The 10th bit position of the P key shall be true."