I'm experiencing the same issue as others here - attempt to preview a file (e.g., Word doc, Excel file, etc.) in Outlook and the Outlook Previewer tries to open and then immediately crashes:

The Word previewer then shows up in the Outlook message pane as being disabled. Re-enabling and trying again yields the same result.
To earlier posted troubleshooting steps, there is no "Unblock" button when downloading an attachment to my desktop and right clicking > Properties, so not sure about that step...
I'm also hesitant about disabling Protected Mode viewing within Outlook - that is not exactly a security best practice (e.g., "My front door deadbolt doesn't work properly - guess I'll just leave it unlocked.")
Interestingly, per the MS support article that was linked to detailing known issues with Windows 10, I amrunning Avast, however I'm running v.11.1.2242 so I would hope that the incompatibility was since resolved since the 10.3 version.
As several others have suggested, I believe this is a legitimate MS software issue that exists with Outlook protected view. Hope it gets added to the backlog (if not there already) and resolved before too long.
Appreciate all the help in this thread thus far.