Step 3: Copy, paste, shrink, loft

Picture of copy, paste, shrink, loft
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Every part of this instructable leads to this step.
If the sketch that you made from tracing or otherwise is copied, it can be used to create a solid feature.  This copied sketch is pasted onto another parallel plane, then shrunk and positioned inside the guide/working axes.  The reason that a duplicate sketch is used instead of a point, is that even though your light may be approximated as a point source, lofting doesn't like it.

Guide lines are produced starting at the light source and leading back to the original sketch (the shadow).  I simply created a point in space that aligned with the utility flashlight bulb and connected it to points on the edges of the sketch using Construction->Work Axis-> Axis by Two Points.

Four lines are enough, assuming they are at the farthest, nearest and widest parts of the sketch.

You may think that projecting a sketch onto another surface will work, but only if your light source is the Sun in which you can very easily approximate the rays as parallel.  For far away lights, this is also true, but your shadow may be blurrier.