Since the source material is inappropriate for a direct data translation, you might consider this adaptation:
Place the PDF image at the correct scale in a plan view.
Draw a mesh to the image extent.
Place a grid over the image.
Locate contour lines adjacent to each grid point.
Apply the height to a new mesh point.
In places where the slope is low, a large grid is suitable.
For steeper places or special site features, make the grid interval smaller to better describe them.
I know it sounds wacky, but this is the way to make a smooth contoured site without excess polygons/nodes, etc.
Dwight Atkinson