What is inside a Word .docx file?

By Check Before Send · Updated 13 October 2026

A zip file of XML parts, and your visible text is only one of them. Microsoft describes the Open XML file formats as an open standard based on ZIP and XML. Alongside the document body, a .docx can hold separate parts for comments, a list of reviewers, document properties, styles and settings.

This guide opens a small Word file the way a program would, lists what is inside, and shows why a document can look clean on screen and still carry more.

What Microsoft says

Microsoft's page on the Open XML SDK describes the Office Open XML file formats as an open, international standard, ECMA-376 and ISO/IEC 29500, and says they are based on ZIP and XML. That is why a .docx can be opened with any zip program.

Microsoft's Document Inspector page lists what Word can hold beyond the text: comments, revision marks from tracked changes, document versions and ink annotations; document properties and personal information such as author, the person who last saved it, and template names; headers, footers and watermarks; hidden text; custom XML data; and invisible content.

What we found inside a test file

We made a small Word file on Microsoft Word 2016 with invented content: a one-line body, an author and company, one comment and one tracked insertion. We opened it as a zip and listed its parts.

Part inside the file	What it holds
The document part	The text of the body, and the tracked insertion
The comments part	The comment's text and its author
The people part	A list of reviewer names
The extended comments part	Whether each comment is marked done
The core properties part	Author, the person who last saved it, and the save times
The app properties part	The company name and the program that made the file
Styles, settings, fonts, theme and relationships	How the document looks and is wired together

The body part was about two kilobytes. Fourteen parts in all, and only one of them is the text you see.

We ran Check Before Send on the file. It listed the author and last-saved-by names, the company, the times, the comment with its text, the tracked change and the reviewer list. We let it make a copy and scanned that a second time: no findings remained. "No findings" means that second scan found nothing, not that the file is guaranteed clean.

What to do

Do not judge a Word file by how it looks. Check the parts it does not show.
Use Word's Document Inspector on a copy, and read the result.
Check the copy you will send with a second tool, since each tool reads different parts.

Limits

This is one small file made in one version of Word. Real documents hold more: images, embedded objects, headers, custom data. We did not open every kind of part, and Check Before Send does not read pictures inside a Word file as text.

Check a Word document before you send it

Drop the file into Check Before Send. It lists each part it found with the values shown, you choose what to remove, and it writes a new copy and runs a second scan on that copy.

The file is read inside your browser and is not uploaded; the Trust Center explains how to confirm that. For one of these parts in detail, see are resolved comments still in a Word document, or browse the other guides.

Sources

More guides

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