I would like to know if there are any 2D/3D CAD software available for Ubuntu 14.04. I'm looking for software that produces DWG/DXF files.
There are lot of apps to use. check this UbuntuEngineering.
But as a first choice I advise you to use FreeCAD.
Quoted from official site:
FreeCAD is a parametric 3D modeler made primarily to design real-life objects of any size. Parametric modeling allows you to easily modify your design by going back into your model history and changing its parameters. FreeCAD is open-source and highly customizable, scriptable and extensible.
FreeCAD is multiplatfom (Windows, Mac and Linux), and reads and writes many open file formats such as STEP, IGES, STL, SVG, DXF, OBJ, IFC, DAE and many others.
You can install it using command line:
sudo apt-get install freecad
Try LibreCAD, here is Wikipedia Link
It supports DXF by libdxfrw.
I use DraftSight on Kubuntu 15.10. Works well and is similiar in layout to AutoCad. Dwg/Dxf supported.