Office 2013 has a new feature that blocks potentially dangerous files. Personally, I find this pretty damn annoying. Office gives you a random error saying “Word experienced an error trying to open the file”.
You can unblock individual files by selecting document properties and clicking “unblock”:
Personally, I want this behavior gone. Open Word, open Settings and locate the Trust Center section. Click “Trust Center Settings” and locate the “Protected View” area and uncheck all options.