Why does XI generate larger PDF than X?

Using Acrobat X, I print a 9 meg PDF from a 30 meg word document on windows.  Using Acrobat XI CC, word 2011 generates a 37 meg PDF.  IN both cases, I am using 300 dpi.  Unfortunately, the quality is also better from X on the PC. 

How do I generate a smaller PDF from word on the mac?