There seems to be a bit of confusion out there as to the difference between PadCAD and PadCAD Lite. Basically, PadCAD Lite is meant to be an evaluation app. It is functionally identical to PadCAD, but it's free. The only difference is that PadCAD Lite does not export or save your drawings, otherwise it's identical to PadCAD.
Once a user evaluates PadCAD Lite and decides she likes the app, she can either upgrade through the app or buy it directly through Apple's app store.