Viewer Pane Showing Code not Preview of PDF File

Up until recently the viewer pane was displaying a preview of PDF files and made it easy to label files from the viewer pane preview. Recently it has stopped showing a preview and is showing a shell icon or a bunch of code. Can anyone help with a solution to this issue, thanks!

(Re-)Install a PDF viewer such as Adobe Reader, PDF-XChange, Sumatra (choose the preview handler option during install), etc.

Make sure it works in File Explorer's viewer as well. If it doesn't then you know the issue is outside of Opus.

I have reinstalled Adobe Reader, The file preview pane in Windows file explorer previews the files fine but still getting code displaying in DO??

Go to Preferences / Viewer / Plugins and configure the ActiveX + Preview + Office + Web plugin.

Does it list Adobe Reader at the top? Is the .pdf extension assigned to it?

The second preview handler is Adobe PDF for Vista (32bit) and it is associated with .ai and .pdf files

Are there any other PDF preview handlers in there? Adobe Reader sometimes installers two, for example, where only one works. (I don't know why.)

Please also try telling your virus checker (and any similar security/privacy tools) to ignore dopus.exe, docsvw32.exe, and docsvw64.exe in case they're blocking access to PDF files. (This has been a problem for several people now.)