Office installation won't open files downloaded from a browser

When I open an office file (I've tested Word / Excel) that I downloaded from a browser (chrome, ff, Edge), regardless of the source (gmail, dropbox web download) I get the following error:

This is on a box with:

• Windows 10 (genuine license)
• Office 360, installed locally - not the online version. (also licensed)

If I take the same word file, open it in another computer and then re-save it in a shared dropbox file, I can open it from the problematic computer no problem. It seems that it only happens when the file is downloaded from a browser on the same computer.

Is there some protection mechanism that I'm unaware of?

Solution 1:

Right-click the Word file that you have problems with, and select "Properties"

When the properties window opens go to the General Tab Click "Unblock" then "OK"

It should work now.

Source