I found a problem using a document that you can download from here:
In few words, opening that document results in a catastrophic crash with program shutdown. This happen either in our application and in your WPF demos.
The document has been generated in Google Drive then converted in docx by Google Drive itself during the download operation.
Deep-tracking the bug, I saw that the problem is probably connected with a CommentRangeStart that hasn't a proper closing CommentRangeEnd marker.
Since I couldn't find the exact point where exception is thrown, please take this indication with a grain of salt.
Even if I know that the problem is generated by a third-party malfunction, it could be a good idea to make your document reader a little more safe.
Thanks for your assistance, bye! :)