Content authors must consider the accessibility of PDF on mobile platforms such as iOS and Android devices. The PDF specification has a well-documented tagging structure that can make a properly tagged PDF document accessible to people with disabilities including people who are blind or visually impaired. The benefits of this tagged structure often are ignored by PDF viewing apps on mobile devices. This situation is not a limitation of the PDF format but a choice that mobile platform manufacturers and PDF viewer developers make. Mobile platform accessibility applications programming interfaces (APIs) are part of the equation and constantly being updated when the mobile platforms are updated. Mobile device users do have a choice of PDF viewing apps, however, no fully accessible solutions are currently available to users who are blind with iOS’s VoiceOver and Android’s TalkBack screen readers. This same challenge occurs for other formats such as Microsoft Word documents.
What PDF features are accessible on iOS and Android mobile platforms?
- The text of a document that is not an image is available to users of screen readers on iOS and Android through several different apps.
- The text however may not appear in the correct order in relation to other text of the document depending on the reader.
- Apps include web view embedded apps, document viewers, and eBook readers
- Apps provide pinch zoom but no reflow of document text to minimize horizontal scrolling
Default PDF document viewers
- The standard iOS preview and iBooks app as well do render text content but no structural information
- The default iOS preview is available in web views embedded within in native apps
- The default Android document viewer provided with Google Drive does not expose any text to screen readers.
- On the iOS platform Reader renders the content in the order that it appears in the Order Panel of Adobe Acrobat Professional. This is slightly different from how screen readers on the desktop such as NVDA and JAWS render content — they use the order of tags in the Tags panel. Ideally the Order panel and Tags panel in Acrobat match — but that is not always the case. The text content itself is primarily what is accessible — other structural and form label information is not available.
- Adobe Reader on iOS has a “night mode” feature which makes the document background black and the text white. This mode may help users with visual impairments that visually read documents.
- On Android no document text is exposed to screen readers.
Third party viewers on Android
- Third party viewers such as PDF Speech to Text Pro allow access to the text content via TalkBack and built-in text-to-speech but do not provide access to structural information such as headings
- Some Android apps and cloud based services will convert PDFs to text — these applications have similar limitations but options vary with some creating HTML equivalents of the PDF. These services may be options for some users especially when PDF documents are linked rather than embedded directly in native platform applications.
What PDF features are generally not accessible?
Structural information such as the presence of headings, lists, tables, and images are not indicated using the default iOS or Android PDF viewer installed with Google Drive or Adobe Reader. In addition, the ability to navigate between units such as lines, paragraphs, headings, lists, etc. are not available. iOS’s preview app does allow direct touch of PDF allowing users to read smaller units of content by exploring the screen. Alternative text for images is not indicated and replacement content formula’s or other non-standard characters or text equations are not presented to users of screen readers. While Adobe Reader on iOS supports forms (iOS Preview does not) the PDF forms do not render accessibility information.
What does this all mean?
Content authors should consider the type and quantity of PDF material that is delivered specifically for consumption on mobile devices. Authors should continue to ensure that the documents are tagged and that the Order panel in Adobe Acrobat Professional properly indicates the reading order of the document. It will likely be helpful to allow users to share the PDF document via medium such as email so users of screen readers can read documents with many structural elements on a desktop or laptop.
Authors may also want to consider whether a PDF file is the best format for this particular content. PDF is great for keeping the look and feel of documents but it may not be the best format for every type of content. Consider why the document was placed in PDF format first — if another format such as HTML will serve the same purpose HTML content can be used. Embedded HTML content (web views) are generally very accessible on the iOS and Android platforms and the default browsers (Browser and Chrome on Android and Safari on iOS) do render HTML structural information to users of screen readers. This area of accessibility will likely continue to evolve and improve in the near term as accessibility APIs on mobile platforms become more robust.