This format is used for data exchange in programs that work with vector graphics from Corel, and also for printing completed designs. It contains image data and also the metadata that describes it. In CMX it’s possible to store layers that can be independently edited. The format is recognized by Adobe Illustrator versions 6-8.
PNG or Portable Network Graphic format is a graphic file format that uses lossless compression algorithm to store raster images. It uses 2 stage compression methods. It is frequently used as web site images rather than printing as it supports only the RGB color model. So CMYK color images cannot be saved as PNG image.