Step 1: Understanding the Concept:
Different software applications use specific, standardized file extensions to save and recognize compatible documents.
Step 2: Detailed Explanation:
- Microsoft Word historically used the ‘.doc‘ (Word Document) extension as its default format from Word 97 up to Word 2003.
- Starting with Word 2007, Microsoft transitioned to the XML-based ‘.docx‘ extension, which remains the modern default.
- Extensions like ‘.msw‘, ‘.wrd‘, and ‘.wor‘ are not standard default extensions for Microsoft Word files.
Therefore, ‘.doc‘ is the correct file extension indicating a Word document.
Step 3: Final Answer:
The file type '.doc' indicates the file is a Word document (Option D).