In a mirror light is highly likely to reflect only in one angle according to the "[law of reflection][1]" ( I have no idea of why that is though ). On a paper it is likely to also reflect in all other directions. Therefore, on the paper, the image of the pencil is drowned out from the light hitting it from all other points in the environment. The light from each point on the pen will hit each point on the paper, and thus contribute to diffuse the image of itself.

With a lens, you will only be able to see the image of the pen on the paper, if the only light that hits the paper is coming through the lens, or at least other light is sufficiently dim. Also the lens must be at the correct distance so it will focus all light coming from one point on the pen to one point on the paper. The reason you see a picture in that case, is because for each point on the paper, there is only one point on the pen (or whatever else is out there) as seen from the point of the lens, that will hit each point on the paper. This means that all light reflected from that point on the paper is coming only from one point on the pen.


  [1]: http://scienceworld.wolfram.com/physics/AngleofReflection.html