.docx

Word Open XML document, Microsoft Word's ZIP-based Office Open XML word processing format

Handled by macOS itself

Format facts

MIME type: application/vnd.openxmlformats-officedocument.wordprocessingml.document
Apple UTI: org.openxmlformats.wordprocessingml.document
Stock Quick Look: macOS renders a preview
Planned approach (census): native-sufficient
Icon hint: unknown
Prevalence: universal

macOS previews Word documents natively

Gotchas: huge embedded media