A file with the .docx file extension is a Microsoft Word Open XML Format Document.

It is the default file format used by Microsoft Word to save documents, replacing the older .doc format starting with the release of Microsoft Word 2007.

Why the "X" Matters

For years, Microsoft used the proprietary .doc format. This older format was binary, meaning all the text, formatting, and images were tightly woven together in a closed system.

The "X" in DOCX stands for XML (Extensible Markup Language). A DOCX file is essentially an open-standard XML document.

This change was revolutionary for several reasons:

  1. Smaller File Sizes: Because it uses ZIP compression under the hood, a DOCX file is significantly smaller than a DOC file containing the exact same content.
  2. Better Data Recovery: In the old DOC format, a single corrupted byte could ruin the whole file. Because DOCX separates the text, styles, and images into different XML files within the archive, a corrupted image won't destroy your text data.
  3. Open Compatibility: Because it uses open XML standards, a DOCX file can be easily read and edited by non-Microsoft software like Google Docs, Apple Pages, and LibreOffice.

The Secret Inside a DOCX File

A DOCX file is actually just a ZIP archive in disguise.

If you take a file named report.docx and change the extension to report.zip, you can unzip it using standard extraction tools. Inside the extracted folder, you will find:

  • A word folder containing document.xml (this is where your actual text lives).
  • A media folder containing all the images you pasted into the document.
  • Various other XML files controlling fonts, themes, and styles.

Note: Changing the extension back to .docx restores the file to normal.

How to Open a DOCX File

On a computer with Microsoft Office: Simply double-click the file. It will open in Microsoft Word.

Without Microsoft Office:

  • Google Docs: You can upload a DOCX file to Google Drive and open it directly in Google Docs for free viewing and editing.
  • Apple Pages: Built into macOS, Pages opens DOCX files natively.
  • LibreOffice / OpenOffice: These free, open-source office suites fully support opening and saving in the DOCX format.
  • WordPad: Windows includes a basic text editor called WordPad that can open simple DOCX files, though complex formatting will be lost.

Converting a DOCX File

If you need to share a finalized DOCX file and want to ensure nobody alters the text, or you want to guarantee it looks identical on every device, you should convert it to PDF.

You can use ToolzStack's DOCX to PDF Converter to easily convert Word documents into secure, universally compatible PDF files.

Related guides: DOC vs DOCX · PDF vs DOCX