cannot open file with CPGZ extension-do I need aftermarket decompression software? Thanks,

Received this .CPGZ 12kb file via email. It certainly should be a legitimate file. When I de-compress the file the new file is also 12kb but does not open.

If I need to purchase a separate utility for de-compressing what do you recommend? I only use this computer for personel use and this is the first time I have had a problem with zipped files in over 2 years. Thanks,