The options listed on this page can be accessed from the Compression window.
Compressed File Extension
The extension entered into this field will be applied to the compressed folder file name. For example, if "rar" is entered for a folder named "Samples," the compressed folder file name will be "Samples.rar."
Note: it is NOT necessary to add a period (" . ") before this extension name. The default extension is "ZIP," which associates the file with a Zip application (i.e. WinZip).