Hello,
How has bad.docx been generated? All DOCX should containt at least one section (w:sectPr tag), but that DOCX doesn't contain any section in the main document file, and also some extra files are missing too in the DOCX.
If you resave it with any DOCX program: MS Word, LibreOffice, Google Docs, a valid DOCX is generated with a section and other files.
Regards.