Are you saying that you can't select Word Document in the Save As dialog box (that the option is missing)? Try repairing your Office installation from Control Panel.

Alternatively, if you are saying that RTF is the default when you Save As, note that you can change this as follows: Click the Office button, and then click Word Options. In the Save category, make sure that "Save files in this format" is set to "Word Document (*.docx)." Click OK.

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Stefan Blom
Microsoft Word MVP