Tested on 2.0 CR3 ifix009.
After uploading a word file to Files, got below error when viewing it:
The file cannot be imported into Viewer. There is something in this file that Viewer does not support at this time. This file cannot be imported.
Opening the file from local word, found there are several comments at the right of the word file. Deleting the comments and tested again, then the file can be viewed successfully.