Windows 10: PDF reader icon appears as picture tumbnail [Acrobat / Nitro PDF]

The Application icon appears as a picture thumbnail rather than the app icon in the taskbar. This is the case with Acrobat and Nitro PDF after checking out.



Please help me resolve this issue,

Thank you in advance.

:)

 

Windows Reader won't display

I tried all of these. The Reader icon appears in the Task bar and shows a preview with mouse hover - but Reader will not open on screen. I have downloaded Acrobat Reader (now my default PDF reader) and it works fine.

 

OneDrive problems on Elite X3

Here is additional information collected since yesterday

Many folders are missing in the "root" OneDrive folder. By searching a subfolder that I want, it is found. The folder shows there are 8 files in it. Opening the folder, I see only 5 Excel files. The 3 pdf files cannot be seen, including the pdf that I aforementioned
opened yesterday.

Searching for the pdf's filename, it is found and can be opened with both Acrobat Reader and Edge

Again, no problem with browsing to folders and files on the Lumia 1020 or via the web. But, on the 1020, when trying to open the pdf file, any of the three, Nitro pdf reader says "Unable to open document!". Adobe Acrobat Reader says "Error opening the document.
The document cannot be opened because it is not a valid PDF document". I have not tried opening the document from the web.

Again, this all started when attempting to open the pdf using the Elite X3.