The extension of a Microsoft Word file can vary depending on the version of Microsoft Office being used. Here are the most common extensions for Microsoft Word documents:

• .doc: This is the legacy file format used by Microsoft Word before the release of Microsoft Office 2007. It is a binary file format and is no longer developed, but can still be opened by the latest version of Microsoft Word.

• .docx: This is the default file format used by Microsoft Word since the release of Microsoft Office 2007. It is an XML-based file format and is the recommended format for saving Word documents. It can be opened by the latest version of Microsoft Word.

• .docm: This is a macro-enabled version of the .docx file format. It can contain macros and scripts and is used for creating documents with complex functionality.

• .dotx: This is a template file format used by Microsoft Word. It is similar to the .docx file format, but is used for creating documents with a predefined structure.

• .dotm: This is a macro-enabled version of the .dotx file format. It can contain macros and scripts and is used for creating templates with complex functionality.

In summary, the extension of a Microsoft Word file can be .doc, .docx, .docm, .dotx, or .dotm, depending on the version of Microsoft Office being used and the type of document being created.