I'm using the LGPO "DefaultAssociationsConfiguration" option, as well as applying the XML using DISM /online.
The XML appears to take, as the icons for .pdfs are changed to adobe reader icons, but I'm still seeing this prompt, any help is much appreciated.

And here is my XML.
<?xml version="1.0" encoding="UTF-8"?>
<DefaultAssociations>
<Association Identifier=".pdf" ProgId="AcroExch.Document.DC" ApplicationName="Adobe Acrobat Reader DC" />
</DefaultAssociations>
/BG
-BrianG (http://supportishere.com)