Is it possible to elevate points that are on the same plane in dxf to heights that are in LAS? I have imported dxf and las file in Arcmap but I need guidance or at least direction where to start looking for solution.
You cannot modify a DXF with ArcGIS. If you import it to a GDB, you can then use Add Surface Information to assign the LAS dataset's elevation to your features.
I solved the problem with importing DXF, creating a raster from LAS dataset and getting the proper height attributes for my points (RASTERVALU).
A caveat was that AutoCAD did not recognize RASTERVALU attribute in shapefile as elevation. To bypass this and import shapefile from ArcGIS, one can use the steps described in "Importing ESRI shape file into Civil 3D shows zero elevations" in Autodesk knowledge base.