Creating accessible links in PDFs
11 April 2010
Summary
Creating accessible links in PDFs is a basic accessibility requirement. This article looks at techniques for tagging links correctly to ensure that they are both keyboard operable and usable with a screen reader. It also looks at, amongst other things, how to make URLs more intelligible for screen reader users.
Tagging
Creating links that are keyboard operable is a single A requirement under the Web Content Accessibility Guidelines (WCAG) 2.0., and is vital in ensuring the accessibility of PDFs. It is especially important for links that make up a document's table of contents – the PDF equivalent of a website navigation system.
For a link to be accessible it must have a specific tag structure consisting of:
- a parent
<Link>tag - one or more child tag(s) containing the link text
- a
Link–OBJRtag which must also be a child of the<Link>tag
The Link–OBJR tag
enables assistive technologies to properly recognise
the link and handle it correctly.
A complete, accessible link tag structure can be seen in Figure 1.
Word, InDesign and beyond
Provided that PDFs are tagged on creation, links originated in Microsoft Word documents will have the required tag structure and will present no problems. However, links currently authored in InDesign will need fixing, as will those found in untagged PDFs.
InDesign originated links
As of this writing, hyperlinks created in InDesign (CS4), when converted to PDF, will produce inaccessible tag structures. An example can be seen in Figure 2.
The problem is that the tag containing the link text
will be created at the wrong level in the tag tree hierarchy.
The tag in question – in this case containing the
word "Hyphenation" – will be created at the same level
as the <Link> tag, rather than being
a child of it.
Such links work with a mouse and appear normally in the tab order but don't work with screen readers.
However, the problem is
easily solved. Just click and drag the link text
tag ("Hyphenation")
and drop it underneath (as child of)
the <Link> tag, at the same level
as the Link-OBJR tag. Figure 3 shows the
same tag tree corrected in this way.
Creating accessible links in Acrobat
Creating an accessible link from scratch in Acrobat Professional is (usually) relatively straightforward. To do so, highlight the text in question, right-click and, from the context menu, select . Choose .
Underlining link text
To underline the link, in the Create Link dialogue box, from the dropdown select . From the dropdown select . Select a colour if required. Once done, navigate to the page you want to link to and click . The correct tags will be created.
Avoid the Create Links from URLs command
If your document contains URLs
which are not active links, you should create
links one at a time using the above method. Resist
the temptation to use the global create links from
URLs command () as
this will not generate the required Link–OBJR tags.
Creating link tags by alternative means
In some PDFs the create link process outlined
above won't work (in some Quark-generated documents,
for example). In such a case it may be necessary to
create <Link>
and Link–OBJR tags by alternative means.
Creating a Link tag
To create a <Link> tag, in the
tags panel select ,
either by right-clicking or from menu.
In the
input field, either
type "L"
or select from
the dropdown.
Create a Link–OBJR tag
To create a Link-OBJR tag, in the tag
tree, either right-click or open the
menu and select .
From the
dropdown select .
Click and then
. A Link–OBJR
tag will be created. If necessary, rearrange the tags
as appropriate.
Making link text screen reader friendly
Because PDFs are often designed to be printed, link text frequently comes in the form of raw URLs which are not particularly screen reader friendly. It is helpful to screen reader users to provide alternative text for such links in order to make them quicker and easier to understand. (In terms of WCAG 2.0 compliance this is a triple A requirement but fixing it is arguably more beneficial than this would imply).
Again, the solution is simple. Highlight the URL and
click Ctrl + C to copy it. In the tag tree,
right-click the <Link> tag
and select
. In the Alternative
Text field of the TouchUp Properties dialogue box,
paste the previously copied URL. Then, for a URL such
as www.ecdp.org, type
"www.e c d p.org" (with spaces between the "e",
"c", "d" and "p"), or for
www.bbc.co.uk, type "www.bbc.co.u k" with a space
between the "u"and the
"k". (Tip: listen to the document with a screen
reader to determine where to place the spaces). Close
the TouchUp Properties dialogue box. These links will
now be voiced by a screen reader in the same way that
a human would read them.
Following these simple techniques will ensure that your links are accessible to, and usable by, the widest range of readers.
Ted Page Director PWS
PDF accessibility services
We specialise in accessible PDF editing and PDF accessibility training, including WCAG 2.0 compliance. Call us on 01932 355 222 for further information.
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