Even though ZIP files are more common, archiving your data in a RAR format is generally considered the better option. Yes, WinRAR is not a free program, but the archives it creates are usually smaller than ZIP files (due to their better compression ratio), and it’s also easier to recover their content from errors.
When archiving important documents, it’s also recommended that you protect them by using a password, which you should then write down somewhere or remember well. Should you happen to forget the password, then you have nothing left to do than search the web for solutions and stumble upon reviews like this one.
Passper for RAR is a simple decrypting program with a very intuitive interface; simply add a RAR archive and give it a go. According to its developers, the application has a 95% chance of cracking the code with one of its four methods of attack.
The first method is called a combination attack, and it involves you choosing certain characters in hope that the program will rearrange them until it gets the password right. Naturally, you should use this method only if you remember a few characters from your lost password. The second method is called a dictionary attack; the program will keep trying to unlock the archive using various words from a dictionary, in hopes that one of them matches.
The third method is the mask attack, which again involves you feeding the program clues, such as password length, types of characters, prefix and suffix. The brute force attack is the final method; it will try all possible combinations, but it will take longer.
The Internet is already filled with programs like Passper for RAR, each of them using almost the same methods of decryption, and even donning similar interfaces. While it may do its job efficiently, you could try a free tool first, if you really need to recover your RAR password.