A Microsoft Word document in the Office Open XML format.
| 0x00000000 | 504B0304 | PK·· | 'PK' — it is a ZIP |
Inside the ZIP: '[Content_Types].xml' plus a 'word/' directory.
A .docx is a ZIP archive of XML parts describing the document, replacing the old binary .doc. It is recognized by opening the ZIP and finding '[Content_Types].xml' plus a 'word/' folder.
Have a file that might be Word document (docx)? Identify it with the File Type Identifier — it reads the magic number locally, nothing is uploaded. Or browse all formats.