First thing to remember is that Office uses the Office XML format. Every .docx document is basically a zip file. The content is stored within, including the document metadata, structure and even some SharePoint metadata.
Now save the file again, place it back into the .zip file. Rename the .zip file to .docx and try to open it. In my case, I got another error message. This one also to do with . I removed that section as well.