Say your business client sends you a bunch of documents compressed in the some format that WinZip cannot open. How would you unzip and extract documents out of this email attachment ?
Either search Google and download a trial version of some zip utility that can deal with the format ? Or ask the client to resend the documents archived in a format that WinZip can understand.
There’s a third option that’s the simplest of all - use Zamzar which a free web based file conversion service.
Zamzar has just added support for archived file formats - you can upload zip files in any format (like tar, cab, 7z, z2, etc) to Zamzar and it will convert them into more common formats like .zip.
The only downside is that RAR is not supported by Zamzar - you can however extract files from RAR via WinRAR or the new Winzip 11 which supports both rar and bz2 formats.
Related: Use Gmail as WinZip