If you're using the integrated Expedition flow then you push changes back from the PCB layout to DxDesigner uisng ECO - Back Annotate or the Setup - Project Integration dialog. You cannot import a netlist directly into DxDesigner other than via EDIF.
If you have local symbols then you can export them as ASCII and import them to a Central Library or use them in a distributed library in the netlist flow. You cannot do this with symbols that already exist in a library and have been instantiated in the design.
Thanks for your response!
Regarding the ASCII export for symbols, I need to export symbol from a schematic as ASCII and need to import it in Library.
Design capture supports to export the schematic symbols as ASCII so we can import all the symbols used in the schematic to new library.
DxDesigner does not have the same capability as DC in this respect, you can only export local symbols to individual ASCII files and then import them to your library.