If the file is a binary file, first check that it has been transferred in binary mode.
If Fetch is set up properly it will normally recognize and decode/expand Mac archive files.

Sometimes Fetch is not able to accurately detect what type of file it has retrieved; although the contents of the file are intact, the file type and creator type, which allow Macs to create the right kind of icon may not have been set properly. Force a binary transfer by checking the binary button. If the icon still does not appear properly you should first make sure that you have software which can open this type of file. If so, one way round the problem is to start off the application and open the file from within the application. If it opens properly resave it using Save As... from the File menu. This should give the file the correct file type, creator type and icon.

If the file is an archive then Stuffit Expander should be able to expand/decode it, even if the icon does not appear properly.

If you use Mac Netscape for file transfers then you should note that Netscape does not know very much about archive file types. It can identify them on the basis of the file extension but cannot decode them itself. In order to decode properly you need to associate Stuffit Expander with the most common archive types. Choose General Preferences from Netscape's Options menu. When the dialogue box appears click on the Helpers tab (see image below). If Stuffit Expander is not indicated for BinHex, Stuffit and MacBinary files, Browse your hard disk to locate it. If you are connected to the College network check the Launch Application button - downloaded files will automatically be decoded by Stuffit Expander as they arrive. If you are connecting to the network via modem check the Save button. You can then disconnect your modem after transfer and decode the file at your leisure, thus minimising the expense of your telephone connection.