My friend have this problem and I fix it by enabling the App that he uses to open document. The easiest way to fix this right away is to uninstall your current word/document apps, and reinstall it which will fix the permissions by default. Here is how I fix it:
1. Open "setting" then select Apps. You will see all of the apps on your system.
2. Look for the Apps that you use to open the document. In my case it was Google drive reader or something like that (I forgot).
3. Then tap on the apps, then tap on the permission and enable all by moving the slider to the left.
Now you are able to open the document.