12+MB is awful large for a 1 page file, there. I printed it to Adobe Acrobat Pro 8 and it only took up 185K. I wonder what’s up with that?
The original image before creation of the .pdf must have been a very large file.
The .pdf quality must have been set very high.
When you sent it to the printer the resolution must have been set for something more reasonable.
High rez color print shop when sent to a printer is often set with no concern for file size.
DPI issue.