If all else fails, the .docx file is actually a ZIP file with several directories in it. One of the files in one of these directories has the text of the document in it, as XML with markup. There are several tags that you should handle as they mark the ends of lines, but most of them mark where autocorrect are marked with various things, or randomly distributed nested tags with 5 levels that format the markup.
(I had to do this manually once on a machine without access to the Internet. Someone saved the file from Office 2011 and wanted to open it in Office 2005 or so in another place in boonies.)
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