Concept:
Microsoft Word is a word processing application that supports a variety of document formats. However, certain file types belong to other Microsoft Office applications.
Step 1: Identify Word-supported formats.
Common formats supported by Microsoft Word include:
• .doc
• .docx
• .pdf
• .rtf
• .txt
Step 2: Understand the .xlsx format.
The extension:
is the default workbook format used by Microsoft Excel.
It stores spreadsheets, formulas, charts, and worksheet data.
Step 3: Evaluate the options.
.docx is Word's native format.
.pdf files can be opened and exported by Word.
.rtf is supported by Word.
.xlsx belongs to Excel rather than Word.
Step 4: Conclusion.
Therefore, .xlsx is not a default Word document format.
Hence, option (C) is correct.