Sadly, one of our customs is still using plant 3D 2011. I don't know if there is any way to import pcf files to plant 3D 2011. There is no trouble to do that in plant 3D 2013. But it seems that the custom would use 2011 for a further time.
I think in autocad Plant 3D 2011 its not possible
you can try using AutoCAD Isometric WS to convert the PCF to IsoDrawing