iOS’s preview app does allow direct touch of PDF allowing users to read smaller units of content by exploring the screen. In addition, the ability to navigate between units such as lines, paragraphs, headings, lists, etc.
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. What PDF features are generally not accessible? These services may be options for some users especially when PDF documents are linked rather than embedded directly in native platform applications. 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.
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.On Android no document text is exposed to screen readers.This mode may help users with visual impairments that visually read documents. Adobe Reader on iOS has a “night mode” feature which makes the document background black and the text white.The text content itself is primarily what is accessible - other structural and form label information is not available. Ideally the Order panel and Tags panel in Acrobat match - but that is not always the case. 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. On the iOS platform Reader renders the content in the order that it appears in the Order Panel of Adobe Acrobat Professional.The default Android document viewer provided with Google Drive does not expose any text to screen readers.The default iOS preview is available in web views embedded within in native apps.The standard iOS preview and iBooks app as well do render text content but no structural information.Apps provide pinch zoom but no reflow of document text to minimize horizontal scrolling.Apps include web view embedded apps, document viewers, and eBook readers.The text however may not appear in the correct order in relation to other text of the document depending on the reader.
The benefits of this tagged structure often are ignored by PDF viewing apps on mobile 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. Content authors must consider the accessibility of PDF on mobile platforms such as iOS and Android devices.