DOCX - Office Open XML Document

DOCX is the document format Microsoft Word has used by default since Word 2007, when it replaced the older binary DOC. The X stands for XML, and it marks a complete change of approach: where DOC was a single opaque binary blob, a DOCX is an ordinary ZIP archive full of readable text files. The format was published as ECMA-376 and later as an ISO standard under the name Office Open XML, which is why other word processors can open and write it.

How a DOCX stores a document

Rename a DOCX to .zip, unpack it, and the document is laid out in front of you as a small website of parts. The text and its formatting live in word/document.xml. Styles, fonts, numbering and footnotes each get their own XML part. Every picture you pasted sits untouched in word/media/ as the image file it always was. A manifest lists the parts and how they relate to each other.

Two useful consequences follow. The ZIP wrapper compresses the XML heavily, so a DOCX is usually far smaller than the equivalent DOC. And because each part is separate, a corrupted image or a broken style does not necessarily take the whole document with it — recovery tools work by rebuilding the archive around the parts that still read.

The flip side is that a DOCX depends on the parts being consistent. An archive whose manifest disagrees with its contents will be refused outright rather than opened approximately, which is why a file that survived a bad transfer often will not open at all.

What metadata a DOCX carries

Word keeps its metadata in two dedicated parts of the archive, and it is more revealing than most other document formats.

The core properties hold the fields you would expect: Title, Subject, Creator — the author — Keywords, Description, and the timestamps Created and Modified. Next to them sits Last Modified By, which names the person who saved the file most recently. On a document that has been passed around an office, that single field can list someone who never appears anywhere on the page.

The extended properties are the ones people rarely think about. Word records Application and AppVersion, so the file names your Office version. It records Company, taken from the installation. It records Pages, Words, Characters, Paragraphs and Lines. And it records TotalTime, the number of minutes the document has been open for editing, and Revision, the number of times it has been saved. A contract that reports a revision number of 47 and 900 minutes of editing time is telling a story its text does not.

Tracked changes and comments are a separate matter again: they live in the XML whether or not the reader has them switched on, so accepting all changes before sharing is not the same as deleting them.

When to use DOCX

Use DOCX while a document is being written, reviewed and revised. It keeps the text editable and reflowable, it round-trips through every major word processor, and it is the format collaborators will expect.

Do not use it for a finished document you are sending out. Layout can shift between word processors and between font sets, so what you see is not guaranteed to be what your reader sees — export to PDF for that. And be deliberate about sharing the DOCX itself: the extended properties above travel with it, and stripping them is a five-second job compared with explaining them later.