There are 4 main methods to converting hard copies to CAD,
Raster: A bitmap image created by scanning drawing into dots. This image can then be imported into CAD. This however is not intelligent data and not straight forward to edit.
Raster to Vector Conversion: A scanned image is traced electronically to produce Vector lines, Arcs and Circles. Vector data is intelligent and can be edited in AutoCAD without any additional add-ons. This method is not very clever with text, solids, dots and dash lines. Very good for a back drop or building outlines. Will convert to approx. 60% to a finished drawing.
Digitising: Either the hardcopy or scanned image is traced manually and thus all components can be converted, structured and layered to give a finished drawing. Accuracy is very dependent on original.
CAD Drafting: Manually reproduce drawings from starch. Is is far the best method but all dimensions, component information and notes need to be at hand. The most time consuming method.