Same problem here...
Placed a PDF as an "External Drawing" on a worksheet. -not big: <100kb
"Store Drawing in the Project File" is ticked
Works fine as trace reference etc. (if a little slow at regenerating).
BUT it absolutely, positively will not print, which is a massive irritation
UPDATE:
I tweaked the external PDF in Adobe Acrobat (7.1) using the "PDF Optimizer" (scanned image) function. After I upated the link in AC12 it now prints....
go figure