Please help me to unrar a file in C# or any free 3rd party dll

UnRAR.dll is a free of charge dynamic-link library (DLL) that can be downloaded from the official WinRAR site.

Thanks for the reply. is there some code sample to extract?

You might skip the middle step and call the winrar.exe with the parameters straight instead of first instanciating cmd.exe

commented: Every single one of your posts link to dapfor.com, and a useless suggestion. -1

is there some code sample to extract?

When you install UnRAR.dll, it has some code samples, including one for C#. Look for UnrarDLL\Examples\C#\ in your Program Files folder.