Problem opening PDF File in default Viewer Adobe from Outlook in Win 10

Question

We have an app through which any user can login and check their mails thru Outlook. All systems are of Win 10.

On all systems the Default app for PDF file is set to Adobe. For some of them, in outlook the PDF file attachment doesn't open by double click or "Click" context menu. I have to click once "Quick Print" and select "Adobe" as default app and then the user can open all the PDF files in Adobe by double clicking it. Those systems are of non-IT people, so they have trouble working with all this. I tried setting Adobe as default PDF viewer as an Admin, and also in Registry extensions, but it doesn't work.

Btw, Edge is not very well supportive as a default PDF Viewer, hence change default app from Edge to Adobe for PDF file

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UPDATE : 2/11/19

Though the default is set to Adobe, on a system, app tries to opens in Edge

Error that Edge shows on opening the PDF file :

Hmmm...can’t reach this page
Try this
Make sure you’ve got the right web address: file:///C:/Users/file.pdf
Search for "file:///C:/Users/file.pdf" on Bing
Refresh the page
Details 
This website could not be found.
Error Code: INET_E_RESOURCE_NOT_FOUND

Any idea of how can I make this work i.e. PDF files be open in Adobe at once from the Outlook opened by our application. Any help is appreciated.

Thanks