Because you want the introduction's page numbering to be capitalized Roman numerals, expand the "Page Number" drop-down menu again, but this time, click "Format Page Numbers." ...

Number styles in Microsoft Publisher allow you to choose a style and format for page numbers in the selected text. Learn how to use this feature.

Change page-number orientation and other header and footer elements when switching between portrait and landscape layouts in Word 2003, 2007, and 2010.