Unlike HTML, in which links are integrated into the text, links in PDF are a type of annotation. Just like highlighter and note annotations, PDF links sit “on top” of the PDF page; they aren’t connected to the text or images on the page at all. Ensuring links in PDF are accessible means ensuring the link annotations are correctly tagged in the tags tree.
Links must be tagged with a <Link> tag, and this tag must be placed in the appropriate location in the tags tree. (Link Tags should not go directly on the root in the tags tree. Instead, the link should be in some other tag like a <P>, <Span>, <TD>, etc.) Also, it is an industry best-practice to ensure the URL is correctly formed (http://www.etc…) and that the link target is valid even though this is not strictly speaking an accessibility requirement.
WCAG 2.0 Success Criterion 2.4.1 requires that a means of skipping repetitive content be provided.
In practice, repetitive content that’s not already an artifact almost never occurs in PDF files. If repeating content is present, include a link preceding (in the tags tree) that content allowing AT users to skip to the next page.
Tagged Links in Acrobat and CommonLook
A correctly tagged link includes both page-content and the link annotation itself. A link tag may have text or images as its contents. The following images show the Acrobat tags tree with a text run and annotation inside of the link tag.
|Link tag in Acrobat’s Tags Tree||Link tag in CommonLook PDF’s Logical Structure Editor|
When created, a link annotation may be tagged separate from its content. In CommonLook PDF, unassociated link annotations are represented by a small, empty box, similar to that of a text run containing just a space character. Place your cursor over the box to see the tooltip and confirm the tag is a link annotation.
Links are created in Acrobat, but they can be deleted in CommonLook PDF. If deletion was unintentional you’ll need to re-create the link using Acrobat.
Make sure to move the relavent text runs inside of the link tag. If you move the tag in the structure tree, be careful to move the link tag, content and annotation together. It’s easy to accidentally select and move the text runs inside of a link tag.
If a link is missing or accidentally deleted it’s easy to create a new one in Adobe Acrobat Professional.
Make sure “tag annotations” is selected before adding new links to the PDF as follows:
- Open the tags panel and right click the top of the tags tree.
A check mark appears next to “Tag Annotations” when this feature is is active.
- Click on tag annotations to activate it.
Now you are ready to add links to your PDF file.
Add a new Link
Once Tag Annotations is enabled you are ready to add new links to your PDF page.
- First, click on Acrobat’s Link tool.
- Acrobat 9: Tools > Advanced Editing menu
- Acrobat X: In the Content panel, “Link”
- Acrobat XI: In the Content Editing panel, “Add or Edit Link”
Link settings (for example the link’s target or visual appearance) may be changed in Acrobat. Changing a link’s settings will not require additional remediation in CommonLook PDF unless the link’s purpose or position has changed.