Given that you mention a user wanting to transfer documents to Google Docs, you could consider working with the RTF format instead. You can also export a docx file to RTF format, work on that and when you are done, import the modified RTF file directly into Google docs.
I suggest this since RTF is also a workable open format: See https://www.safaribooksonline.com/library/view/rtf-pocket-guide/9781449302047/ch01.html. Based on that reference, you can generate this simple (ascii) output:
{\rtf1\ansi\deff0 {\fonttbl {\f0 Verdana;}}
\f0\fs16
Hello World!
}
and save it as a file with the .rtf extension.
