I was having a similar problem in ACAD 2009 today, and previously never had the issue in older versions (was working in 2007 until recent weeks). Changing the default PDF dpi from 1200 to 300 solved the problem for me as well. I had to restart AutoCAD after making the change to the pc3 file - I don't know why, but once I did, hours long headache appears to be solved. Thanks for the tip.
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