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The following command will fix the situation, where PDF documents will always open in the default PDF reader, but previewing won’t work anymore
Get-SPWOPIBinding –Application “WordPDF” | Remove-SPWOPIBinding -Confirm:$false
The following fixed all my problems Your PDF documents will be opened in the default PDF reader, the preview will work and Word Web App will present the PDF documents in the “embedview”.
Get-SPWOPIBinding -Action “embedview” -Application “WordPdf”| Set-SPWOPIBinding -DefaultAction