We write out the coordinate system of the data in a way that the PDF understands. It is true that if you want to do Measuring and Commenting, you need to do the open/close with Acrobat Pro. Which, as far as we can determine, is the same situation if you use ArcGIS directly to produce Geospatial PDFs.

@James/others — I’m very interested in what applications people come up with for the Geospatial PDF output. In many ways I think this is the sleeper addition to FME this time around, that has a wide range of interesting applications. Not quite as big a deal as what KML did to allow publishing of geospatial to the masses, but in a similar league. So if any of you have a chance to give it a spin, let me know how it works out for you. We’re already looking at a number of additional enhancements to this format (you can’t stop progress) and I’d be interested in what your applications would benefit from.