What is the best form to convert a .dwg file to so that the contractors can snap, inquire, etc. the features of our Autocad 2009 file but cannot steal the blocks/design out of the drawing? We do Civil site plans in ACAD2009 and have to send out plans for concrete contractors, site utilities providers, etc. and they need to snap distances, see elevations, identify bearing/distances, etc. but we are concerned about the copyright of our engineered drawings of the base plan without an engineer's seal. Is DWF the best format to save this dwg to in order to give them access without them being able to alter or pilfer the design dwg?