28 October 2021 | Ted Page
The term “interactive PDF” usually refers to the use of navigation links that repeat on each page, or next/previous page navigation buttons. If you are going to include such navigation in a PDF, you will need to be aware of the potential pitfalls, and how to avoid them.
The problems of repeating links
At the root of the problem is the fact that in a PDF you can’t hide links from screen readers. Unless a means to skip the navigation is provided on each page (see below), screen reader users may be forced to read the entire navigation section on each page.
This, of course, would be a serious usability problem as well as a fail against the ‘Single A’ WCAG requirement to ‘bypass blocks of content that are repeated on multiple pages’ (SC 2.4.1).
But not only will you need to know how to skip blocks of navigation links, you will also need to know how to create the navigation links themselves properly in InDesign. Doing so is relatively straightforward, but get it wrong and you will be in for a lot of time-consuming, advanced-level correction work in Acrobat.
But before we look at how to make such links accessible in InDesign, we need to talk about buttons.
The problems of buttons
The use of buttons to create next and previous page navigation is a non-starter. Like links, buttons cannot be hidden from screen readers. But more seriously, they disable reflow view (Ctrl/Cmd + 4 to toggle reflow on or off). There is no workaround for this.
The ability to reflow text is, of course, a ‘Double A’ WCAG requirement (SC 1.4.10). For this reason, buttons should never be used for navigation. Use links (or HTML) instead.
Creating accessible repeating navigation links in InDesign
In InDesign you will typically add the text for the navigation via master pages. These will then need to be linked to the appropriate places within the document. Make sure you link, using hyperlinks and hyperlink destinations, to the start of the main content on each page and not to the top of the page.
Once this is done, the text and links will need to be released from the master pages (Ctrl/Cmd + Shift + Click). If you skip this step the navigation links will not be tagged at all when you export to PDF. However, do it correctly, and InDesign will do all the hard work for you in creating the required <Link> and <Link-OBJR> tags as well as tagging the link text itself.
Providing skip links
The above steps will get you most of the way in making your navigation accessible, but you will also need to provide a ‘skip link’ before the navigation on each page for those readers wishing to bypass the navigation section altogether.
In theory it is possible to provide an invisible ‘skip to main content’ link at the top of each page. However, doing so will require some quite involved JavaScript to make the link text visible when the link receives focus, and invisible again when it loses focus. This will have to be done in Acrobat not in InDesign.
A more practical solution might be to include next/previous page links which could be made to do the same job, but much more simply. For example, the next page link on, say, page 2 will bypass the navigation at the top of page 3 and go directly to the start of the main content on that page (page 3). Again, you will need to use hyperlinks and hyperlink destinations to do this job in InDesign.
Conclusion
If you are going to include repeating navigation links on each page, you must:
- ensure that those links are accessible, and
- ensure that navigation blocks can be skipped.
In some PDFs, on-the-page repeating navigation may be OK to use, whilst in others, for example when sentences or paragraphs break across page breaks resulting in navigation or skip links appearing in the middle of sentences or paragraphs, maybe not.
The PDF format includes several purpose-built, accessible navigation mechanisms such as tables of contents, bookmarks, and A to Z indexes. In some cases, you might want to consider using these rather than trying to mimic web-style navigation. However, with care, repeating navigation links on each page can be made accessible, depending on the nature of the content, and as long as you don’t use buttons.
InDesign accessibility training
The above is taken from our Accessible PDFs from InDesign training course.