What is a DOCX file?

The DOCX file format stands as the modern, open standard for Microsoft Word documents, revolutionizing digital document creation upon its launch with Microsoft Office 2007. This pivotal update marked a fundamental shift away from the legacy, plain binary structure of the older DOC format. Instead, DOCX leverages a sophisticated hybrid architecture built on a combination of XML and binary files, compressed within a ZIP container. This innovative structure enhances data recovery, reduces file sizes, and improves interoperability. Due to this core technological change, DOCX files are fully compatible with Word 2007 and all subsequent versions, but they cannot be natively opened by earlier versions of MS Word that were designed exclusively for the proprietary DOC file extension.

Brief History

After Microsoft opened the specifications for the DOC file format, it was easy for its competitors to reverse engineer the format and provide the same support in their own applications. In addition, the competition from Open Office in the form of its Open Document Format, compelled Microsoft to adopt more open and wide standards. It was in early 2000 when Microsoft decided to go for the change to accommodate the standard for Office Open XML. Documents under this new Standard were given .docx extension, the “X” being for XML. By 2007, this new file format became part of Office 2007 and is carried on in the new versions of Microsoft Office as well. The new file type has added advantages of small file sizes, fewer changes of corruption and well-formatted images representation.

Key Characteristics of DOCX Files

Characteristic	Description
File Extension	.docx
Full Name	Microsoft Word Open XML Document.
MIME Type	application/vnd.openxmlformats-officedocument.wordprocessingml.document.
Primary Use Case	Small file size, improved data recovery, and enhanced security
Primary Software	Microsoft Word (2007 and later).
Key Advantage	Small file size, improved data recovery, and enhanced security.
Macro Support	No (Macros require the separate DOCM format).
Open Standard	Yes (ECMA-376, ISO/IEC 29500)

DOCX File Format Specifications - More Information

A Docx file comprises of a collection of XML files that are contained inside a ZIP archive. The contents of a new Word document can be viewed by unzipping its contents. The collection contains a list of XML files that are categorized as:

MetaData Files - contains information about other files available in the archive
Document - contains the actual contents of the document

Metadata Files

Microsoft Word uses these files to find the relationship between files and to locate the document contents. When a Word document archive is extracted, it contains a number of such files as detailed below.

Relationships - _rels/.rels

This file contains information that tells MS Word where to look for the document contents and other references. Each relationship is identified by a unique relationship id and specifies the referenced XML file as target. A sample relationship file is shown as follow:

<Relationship Id#"rId1" Type#"http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument" Target#"word/document.xml"/>.

Content Types

A document can contain several media types inside like images, themes, word art, etc. The [Content_Types].xml contains information about such media types present in the document. Contents of a such an XML file are shown as follow:

<Override PartName#"/word/document.xml" ContentType#"application/vnd.openxmlformats-officedocument.wordprocessingml.document.main+xml"/>

References To Resources - _rels/document.xml.rels

Information about resources, such as images embedded in the document, are referenced in this XML file.

Main Document Contents

This refers to the main XML file of the archive that contains the document’s text content. This content is represented by variety of nodes as per the OpenOffice XML specifications. Mostly the contents of this file consist of Paragraphs and Tables, though their can be other nodes as well.

File Format Nodes

The main document.xml file is a collection of nodes for representation of the overall contents of a file. Each node has a start and end that encapsulates either further nodes or the contents. A simplified example of such an xml file is as follow:

<w:document>
   <w:body>
       <w:p w:rsidR#"005F670F" w:rsidRDefault#"005F79F5">
           <w:r><w:t>Example Document</w:t></w:r>
       </w:p>
       <w:sectPr w:rsidR#"005F670F">
           <w:pgSz w:w#"12240" w:h#"15840"/>
           <w:pgMar w:top#"1440" w:right#"1440" w:bottom#"1440" w:left#"1440" w:header#"720" w:footer#"720"
                    w:gutter#"0"/>
           <w:cols w:space#"720"/>
           <w:docGrid w:linePitch#"360"/>
       </w:sectPr>
   </w:body>
</w:document>

Following is the information about some of the nodes contained in a DOCX file for representation of contents.

<w:document> - Represents the root element of the main content of the file.

<w:body> - Represents the body of the document which can comprise of many other element nodes such as paragraphs, tables and sections.

Paragraphs

A paragraph is the main content holder within a document. It is represented by <w:p> element within a document. A paragraph further consists of one or more runs <w:r> that contains the actual text of the paragraph. In addition to runs, paragraphs may also contain other document elements such as hyperlinks, comments, etc. An example paragraph structure is as shown below:

<w:p>
<w:pPr>
<w:pStyle> w:val#"MyStyle"/>
<w:spacing w:before#"120" w:after#"120"/>
</w:pPr>
<w:r>
<w:t xml"space#"preserve">A paragraph is main container in a document that further consists of a one or more runs where the text of paragraph is actually contained.</w:t>
</w:r>
</w:p>

DOCX FAQs

Is DOCX a File Extension? - DOCX is used as file extension to represent Microsoft Word 2007 and later file formats used to store Word files. It also tells your OS that this DOCX file requires Microsoft Word 2007 to open it and show its icon.
Is DOCX same as Word - DOCX is a file format used by Microsoft Word to save documents in Open XML format. Word, on the other hand, is an application software by Microsoft Office that also supports other file formats such as DOC, DOT, DOTM, and others.
What is difference DOC and DOCX - DOC is word file saved in Word 2007 and earlier file format. DOCX is based on Open XML file format supported by Microsoft 2007 and later versions. Check Differences between DOC and DOCX for more details.

FAQ

Q1: What is the difference between DOCX and DOCM?

A: DOCX files cannot run macros and are generally safe, while DOCM files are specifically designed to contain and execute VBA macros, posing a potential security risk.

Q2: How can I open a DOCM file safely?

A: Open it with a modern version of Microsoft Word, but do not click “Enable Content” unless you absolutely trust the source and need the macro functionality.

Q3: Can I convert a DOCM file to a DOCX file?

A: Yes, in Microsoft Word, use “Save As” and choose the “Word Document (*.docx)” format; this will remove all macros, making the file safer but also disabling any automation.

Q4: Why would a legitimate business use a DOCM file?

A: Businesses use DOCM files to create intelligent templates that automate complex tasks, such as generating contracts, populating reports, or performing data validation in forms.

Q5: What should I do if I accidentally enabled macros in an untrusted DOCM file?

A: Disconnect your computer from the internet immediately and run a full system scan with your antivirus software, as your system may have been compromised.