The best choice is actually Bluebeam Revu as it also allows you to collaborate on the PDF with multiple users simultaneously with mark-up functions. You can get a 30 day trial of the CAD version (necessary to work with the Revit Plug-In from http://www.bluebeam.com/us/partners/network/hagen/cad/
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The model can be opened via IE8 or just download a DWFx viewer add-on for Firefox. See http://usa.autodesk.com/adsk/servlet/item?siteID=123112&id=14683283&linkID=9338138.