DOCX File Format (.docx)

A DOCX file is a ZIP archive of XML documents conforming to the Office Open XML standard (ECMA-376 / ISO/IEC 29500), a structure with nothing in common with the single opaque binary stream the older .doc format used.

.docxDocuments

DOCX at a glance#

Full name	Microsoft Word (Office Open XML)
File extension	.docx
Category	Documents
Developer	Microsoft
First released	2007
MIME types	application/vnd.openxmlformats-officedocument.wordprocessingml.document
Compression	Lossless
Specification	ECMA-376 / ISO/IEC 29500 (Office Open XML)
FileFlip support	FileFlip reads and writes this format

What a .docx file can hold#

These are the things a DOCX file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.

Embedded metadata	Yes
Multiple images or pages	Yes
Selectable text	Yes
Encryption	Yes
Human readable	No
Comments	Yes
Schema or validation	Yes

Strengths and limitations of DOCX#

What DOCX does well

Structure like headings, lists and styles survives conversion because it's tagged in the XML rather than only implied by appearance
Opens in Word, LibreOffice Writer, Google Docs and Apple Pages without a plugin
Track changes and comments are stored as their own XML elements, separate from the visible text, so they travel with the file rather than getting baked in
A ZIP of readable XML parts, so software other than Word can generate or repair it without reverse-engineering a binary format

Where DOCX falls short

Most Word installs still write the Transitional conformance class, which keeps legacy binary-compatible quirks that the cleaner Strict class was meant to retire
Complex layouts built with manual spacing and floating text boxes convert unreliably to other formats
Macros live in the separate .docm variant, so a plain DOCX file can't carry them
Fonts aren't embedded by default, so a document opened without the original fonts installed silently substitutes different ones

Use DOCX for any document that still needs editing, since headings, styles, comments and track changes all round-trip between word processors that support Office Open XML.

Convert DOCX to PDF once the document is finished and needs to look the same for every reader, or to ODT when the destination is LibreOffice or an organization whose policy requires the open standard.

How to open a .docx file#

A .docx file opens in the programs below, grouped by the platform you are on. If you would rather not install anything, FileFlip converts DOCX into a format your machine already opens, and it does it in the browser tab rather than on a server.

Platform	Programs that open it
Windows	Microsoft Word, LibreOffice Writer, WPS Office
macOS	Microsoft Word, Apple Pages, LibreOffice Writer
Linux	LibreOffice Writer, OnlyOffice
iOS	Microsoft Word, Apple Pages
Android	Microsoft Word, Google Docs
Web	FileFlip, Google Docs, Microsoft Word Online

DOCX questions people ask#

Is DOCX the same as the old DOC format?

No, DOCX and DOC are genuinely different technologies. DOC, used through Word 2003, is a single proprietary binary stream that only Microsoft's own code could reliably parse. DOCX, introduced with Word 2007, is a ZIP archive of XML files following the Office Open XML standard, which is why other applications can read and write it without reverse-engineering Microsoft's format.

Can I open a DOCX file without Microsoft Word?

Yes. DOCX is an open, published standard, so LibreOffice Writer, Google Docs, Apple Pages and several other applications open and save it natively. Formatting fidelity is generally very good for standard documents, though features specific to Word can shift slightly in another application.

Why does renaming a DOCX file to .zip let me open it as an archive?

Because a DOCX file literally is a ZIP archive. Renaming the extension to .zip and expanding it reveals folders of XML files for the document's text, styles, images and metadata, which is the actual internal structure Word writes to disk.

Does converting DOCX to PDF preserve the formatting exactly?

Yes, essentially exactly, because that conversion runs in the easy direction: DOCX describes flowable text with styles, and PDF freezes whatever that text currently looks like into fixed positions. The reverse conversion, PDF back to DOCX, is the hard, lossy one, since it has to guess structure from fixed positions instead of reading it directly.

What happens to comments and track changes when I convert a DOCX file?

It depends on the destination format. Converting DOCX to PDF can keep comments as PDF annotations, but converting to plain text or Markdown drops them entirely, since neither format has a place to put a comment that isn't part of the document body.

Converting DOCX files#

Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.