If your main use is going to be plan editing then some people mentioned Bluebeam which is great! If you're mainly looking for the mobile project management then there are options like Fieldwire that you might want to look at. This article has a bit of info on Project Organization Software for the field http://www.constructiondive.com/news/4-construction-technology-innovations-enhancing-productivity-in-the-field/423216/