Applies to: ZWCAD 2015
If you need to convert PLT file to DWG file, firstly the PLT file must be of HPGL/1 standard, that is, the PLT file must be created by some old styles plotter, only under this condition, the command PLT2DWG can convert it to DWG.
Currently most of the main-stream plotters has already apply the HPGL/2 standard, and the PLT files created by which cannot be converted to DWG file. So we can say the command PLT2DWG has limitation.
You can also try the ViewCompanion to open the PLT file, this tool is not free.
If you want to plot out or import into ZWCAD, you can try the free tool HPGL2-to-PDFconverter that can convert plt files (HPGL2 format) to PDF, then you can import the PDF into ZWCAD