If the file is encrypted, you will need the password provided by the creator, which can be entered using 7-Zip or WinZip.
Right-click the file, select your archiving program (e.g., 7-Zip), and choose "Extract Here". Troubleshooting
To provide a more detailed report on the contents of the file, I would Is this a ? A document archive ? Did it come from a specific website or forum ?