Question

how can i open winrar file without having it's password ?

Answer 1

It uses encryption, so you need to break the encryption which basically means find the password. Depending on the security level of the password that can be done in minutes or take a few years or if someone got creative and adapted a properly formed one time pad into the rar code then all the computers in the world could take a few hundred years and not get there.

Answer 2

totally correct on the encryption side, however there are tons of cracking tools.