Yes, you can.  A Word document can be divided into sections, using something
called section breaks.  Each section can have a different set of margins,
paper size, headers and footers, and various other types of page formatting.
So to have a different size page in your document, insert a Next Page
section break, using Insert>Break, both immediately before and immediately
after that page.  Then, with your cursor positioned on that page, go to
File>Page Setup, change the paper size, make sure the 'Apply to' setting is
set to 'This section only', and click OK.  Now you are set!

Regards,
Chad DeMeyer