PDF Portfolios are based on Flash. It's impossible to view them without Flash. In Acrobat/Reader 9 and X, Flash was built in. In Acrobat/Reader XI, it must be downloaded for security reasons. (I believe the reasoning is that, because only a minority of Acrobat/Reader users use PDF Portfolios or features which require Flash, it's not wise to expect people to do the frequent security updates in Acrobat/Reader that Flash requires.)
