When you open a PDF file on a mobile device by using Microsoft SharePoint and Office Web Apps or Office Online Server, the mobile browser displays the following error message:
"Viewing .PDF files has been disabled in Microsoft Word Mobile viewer."
This problem occurs because PDF viewing on mobile browsers is not supported in Office Web Apps or Office Online Server.
The "MobileView" action was removed from the available Web Application Open Platform Interface Protocol (WOPI) actions for the WordPDF application. Also this feature is not available for Office Online Server.