If you accidentally forget the open password of rar file, then there is basically no possibility of unlocking RAR password. The unique anti-cracking algorithm of RAR file makes decryption very difficulty and time-consuming.
But if the publisher didn't offer the password, then it would be very difficult to open a password protected rar file without password. But they do come with attached with keygen which allows you open a password protected rar file with knowing password. Most of the RAR files that you download form software distribution websites are available locked for an extra security. But don't feel disappointed about it for we all face these situations at one point of time or other. Got a new RAR file but found it locked with a Password protection? And you don’t have the password anywhere in your downloaded file or received email? Indeed it is a matter of concern.