Silktide performs a number of accessibility checks on PDFs, see below for the complete list and explanation of each check.
Ensure the first heading in a PDF is a H1 – WCAG A 1.3.1
Type: Automated
The first heading in a PDF document should be a Heading 1. Failure to meet this indicates that either:
1. Headings are incorrectly structured (e.g. H2 before H1)
2. Or, the order of elements in the PDF is incorrect
Ensure PDF headings follow a logical order – WCAG A 1.3.1
Type: Automated
Headings in a PDF should follow the sequence Heading 1 > Heading 2 > Heading 3 without skipping intermediate headings.
It is acceptable to ‘go back’ to previous styles/headings, but the sequence should then continue without missing headings.
Ensure long PDFs use bookmarks to aid navigation – WCAG AA 2.4.5
Type: Automated
Bookmarks (also known as outline entries) should be applied to long PDFs to provide a hierarchical overview of the document to help aid navigation.
WCAG guidelines do not specify how many pages are required to be classified as a long PDF. Because of this Silktide treats PDFs of 21 or more pages as long. This matches Adobe Acrobat’s interpretation.
Ensure PDFs specify a default language – WCAG A 3.1.1
Type: Automated
PDFs should have a default document language set to help render text accurately and help screen readers pronounce words correctly.
Specify headings for every PDF – WCAG A 1.3.1
Type: Automated
PDF files should have headings.
Tag all PDFs – WCAG A 1.3.1
Type: Automated
PDFs need to be tagged in a valid reading order for accessibility. See Adobe’s guide and WCAG for advice.
Ensure PDFs have a title – WCAG A 2.4.2
Type: Automated
All PDFs must define a valid title. This must not be confused with the file name. See PDF 18 for details.
Ensure PDFs are machine readable – WCAG A 1.1.1
Type: Automated
PDFs need to be machine readable for accessibility software to be able to access them. Scanned documents or password-protected ones are usually not machine-readable.
Improve weak PDF titles – WCAG A 2.4.2
Type: Automated
All PDFs must define a descriptive title. See PDF 18 for details.
Check PDFs have sufficient text contrast – WCAG A 1.4.3
Type: Assisted
To comply with WCAG AA, the color of text must sufficiently contrast with its background color, so that people with moderate visual impairments can read it.
The contrast ratio must be at least 4.5:1 for body text, and 3:1 for large text.
Ensure PDF content is in a meaningful sequence – WCAG A 1.3.2
Type: Assisted
Headings in a PDF should follow the sequence Heading 1 > Heading 2 > Heading 3 without skipping intermediate headings.
It is acceptable to ‘go back’ to previous styles/headings, but the sequence should then continue without missing headings.