Open PDF's with Adobe instead of Office Web Apps

SharePoint / PDF Default Application

Adobe PDF files can be opened with either Office Web Apps (browser) or one of the Adobe pdf viewers. Powershell will assist.

Change default PDF Application from Office Web Apps to Adobe Viewer

To adjust the binding so that smartphones won’t try to view PDFs in Word Web App (but other devices will continue to), enter the following command and then press Enter:

Get-SPWopiBinding -Action "MobileView" -Application "WordPDF" | Remove-SPWopiBinding -Confirm:$false

To remove the binding altogether so that PDFs open in the default PDF viewer on all devices, use the following:

Get-SPWOPIBinding –Application "WordPDF" | Remove-SPWOPIBinding -Confirm:$false

Change Default PDF Application from Adobe to OWA  

Get-SPWOPIBinding –Application "WordPDF" | Remove-SPWOPIBinding -Confirm:$false

New-SPWOPIBinding –ServerName "<OWAServerName(ex: server.corp.Contoso.com)>" –Application "WordPDF" -AllowHTTP

Source:

https://blogs.technet.com/b/office_resource_kit/archive/2013/07/24/control-whether-pdfs-open-in-word-web-app-or-the-default-pdf-reader.aspx