Some Polylines from DXF files can be imported as TAD objects. However you need to ensure they are made in the following manner

1. The polylines must be closed
2. The polylines must have straight edges only
3. The polyline is given a Hyperlink; the text of which is the name of the objet. Such DXF files can easily be created in Nanocad 5 (free version)
4. The polyline is placed in a layer which becomes the class
5. Try to make the polyline only in layers (classes) they belong to. Polylines made on Layer 0 are to be avoided

This is possible due to a utility included in the bin folder of your installation. It is a console (Command line driven) program. It is called dxftotadshapes.exe

Usage:

Two arguments needed:

    DXF_FILENAME OUTPUT_FILENAME

The objects found in the DXF will be created inside the opened model within TAD. The data is saved to OUTPUT_FILENAME

Note: This program is called silently by TAD when you invoke the “Invoke objects from DXF…” dialog, so you don't have much use of this unless you want to do some specific debugging. There is already a DXF file called testplines.dxf in the TAD Designer Lite installation (in same 'bin' folder) You can try that DXF file in Nanocad Free 5.0 CAD Software and check how it was created

IMPORTANT
Due to some silly problem with some anti-virus software, this utility is NOT included in the default installer of TAD. This utility was created with a new language called RED – www.red-lang.org

For some reason, some anti-virus software do not recognize the signature produced by that compiler; and falsely marks the executable as problematic.

You can download it separately from here: https://tad.in.net/dxftotadshapes.zip The README.txt file in that zip file explains the situation we faced; and if you feel that you can try it out then do so as per your own discretion. (Note that we are quite sure that it has no virus or other problems)