You can try this too, intended for educational purposes only. I am not responsible for any damage caused.

As per some documents online, you can extract contents of .docx file into a folder, add any file(I added 7-zip installer file) into it, and compress the file back to .docx.

Aforementioned process was done entirely using 7-zip, uploaded to OneDrive, downloaded, extracted the installer and ran the installer.

Just written-PoC using GUI only. No codes involved. TODO: Study(?) .zip, .docx and LZMA