The password can contain letters, figures, and symbols. The longer is the password, the stronger is the encryption. The password shall not be the word from a dictionary. Such password can be "guessed" by the utility program in 1 (!) second. I would suggest the random text string from small and capital letters, figures, and keyboard symbols not less than 14 characters. Such a good password would be difficult to find out even with the supercomputer.
If the password is lost or forgotten, there is absolutely no way to recover the text from the encrypted text, as it is the strong encryption.
This encryption can not be broken in the direct meaning of this word. Still there are methods, how any encryption can be compromised. For example, the key-logging software can be installed on the computer to log every keystroke, etc. You can protect against key-logging spying by using the virtual onscreen keyboard, available in this implementation. This makes this cryptographic system practically impregnable.
The advantage of this encryption program is that it is accessible at any computer connected to the Internet. No installation is needed.