One of my colleagues wanted to change the behavior of SharePoint 2013 so that viewing a PDF in a document library on a mobile device opened the PDF in Adobe Acrobat Reader rather than the Word Office Web App.
A post on the Office IT Pro blog (link) indicated that this was possible and just required us to run:
Get-SPWopiBinding -Action "MobileView" -Application "WordPDF" | Remove-SPWopiBinding -Confirm:$false
Unfortunately this didn’t work for us and when I ran Get-SPWopiBinding -Action "MobileView" -Application "WordPDF" nothing was returned. Further investigation reveals that the MobileView action was removed from SharePoint 2013 in the October 2013 Cummulative Update.
Looks like changing the default behavior is going to be for all devices but I will update this post if I find out anymore.