Alright I actually did this successfully a few months back following these steps http://www.avenza.com/resources/blog/2016/12/06/exporting-qgis-avenza-maps.
Now when I bring the map into Avenza, I get a "Map Not Referenced"
Now I have no clue what I am doing wrong. I have tried and tried. I have unistalled and reinstalled. Tried to export as image then convert format.
A strange thing to note, I can not select reference map under Print Composer-> Export Settings -> Reference Map.
Best Answer
Using QGIS 2.18.13 installed using network installer I was able to export my Print Composer map to a geoPDF that is recognized by Avenza 2.3.x as georeferenced. When in Print Composer I select the Composition tab, and in Export Settings set the Reference Map as the selected map, e.g. Map 0. Then export as a PDF.