That is what I assumed/hoped as well.
When I build our plugin with READER_PLUGIN defined I get the following type of error:
Error 54 error C2065: 'PDEContentGetNumElemsSELPROTO' : undeclared identifier C:\src\map2pdf\geoapi\SelectionServer\SelectionServerTool.cpp 64 1 geoapi
Which unfortunately is in agreement with what the doc says:
Product availability: Acrobat, PDFL
We're using SDK 9 with VS2010 if that matters.