I'm currently working on a utility software, file compression, with VB.Net.
And using an open source library to compress and decompress files - DotNetZip - and already running.

My friend told to make it unique and not traditional, that I make the output compressed files cannot be opened with other compression software. Now my question is... is it possible that way? Using an open source library which the output format is ".zip"?

I first thought that changing the file extension of the compressed file to unknown format so it can't be opened when you try to decompress it, unfortunately, using the "Open With..." function of windows it could still be decompressed.

I'm running out of ideas and really need some people's help.

Is it really possible? OR what other features can I add that WinZIP doesnt have yet? I compared my work to WinZip since the same output is ".zip".

Thank you so much for your ideas

To make it really unique you would have to come up with a new compression algorithm. See Data compression what exists and come up with a new idea. After that you have to implement the algorithm and compare it's "efficiency" with other methods/applications, like 7z, WinZip, WinRAR etc.

I don't quite get your friend's point why it should be unique? And I'm not talking about file extension although I wouldn't use "zip" extension because that's used in WinZip and PKZip.

Well, good luck anyway...