It sounds like your iMac has a conflict between the Adobe Reader and the Printer. Try this simple fix:
First open the flyer in Adobe Reader (version 8 or higher), then click File and Print. Then click the Advanced tab and check “Print as Image” then OK, then under Page Scaling choose “Fit to Printable Area” (you can try other settings too but “fit” should work best), then click Print.
This should fix the problem. You can also try saving the flyer to a thumb drive then opening it on another computer or taking it to a local print shop (they should be able to open it no problem).
These screenshots show you what I mean: