Cannot View PDF Files in Viewer Pane

I cannot view any PDF files in the viewer pane. I have tried Adobe Acrobat Viewer and several other PDF programs such as Soda and Ashampoo. All I see in the PDF viewer is code.

I am able to preview PDF files in Windows 10 Explorer.

Any help would be appreciated.

My version is:
Directory Opus Pro 12.21 Build 7478 x64
OS 10.0 (B:20211 P:2 T:1) SP 0.0

Please post a screenshot of the ActiveX + Preview + Office + Web plugin under Preferences / Viewer / Plugins. For example:

While there, try clicking the Defaults button in the lower left.