I am looking to create 3D terrain from a contour map that I have (originally inside a PDF). The contour lines are able to be viewed as paths in Adobe Illustrator. There are two types of lines: 7m and 2m intervals, which are the same color, but have different weights (the 7m contour lines are twice the weight of the 2m contour lines). If it might be useful to know: according to its metadata, the PDF appears to have been exported from AutoCAD. The contour lines (as paths in Illustrator) can be exported as .DXF, .DWG, and several other formats.
What is the simplest/easiest way to create a 3D model with the available data? Can it be done with free/open source software?
I can't seem to find anything that matches my situation.
I'm looking to create a 3D representation from the contour lines in order to render it in a 3D modelling program - something like a .DAE format (or similar).
The (near to) end result will look like: