I have the same problem, I'm currently running AS2012 standalone version.
I did ask graitec UK about this but didn't really get any feed back on this issue, other than it might be the PDF software creater I'm using ( PDF factory pro )
The only way I can reduce the file size was to, explode the dwg file, then open it in Autodesk's trueview and print to PDF from there ( using PDF factory pro ) which made the file to a normal size expected.
Very long winded and sucks when you have revisions.
Hope you get better feed back than me.
Regards
Danny