You have to remove the security settings first. I assume the file limits content extraction, that's the reason why you cannot convert it to a Word file (you would also not be able to e.g. copy and paste content into a different document).
To access the content, open the file, then bring up the content properties, go to the Security tab and chagne the security method to "No Security". Save the file under a new name and try to conversion to MS Word again.