From the WD community site:
"Unfortunately, There is not an application or software that allow you to bypass the password of WD Smartware. Not WD have an way to retrieve your password.
You can regain access to your drive, but in order to do so, you will need to erase it; this will delete all data from the drive, and unfortunately this cannot be avoided.
Please visit the link below for information on how to erase your drive, scroll down to the "Failed Login" section and follow the instructions provided.
Answer Title: How to set up security in order to lock and unlock a WD (+ SmartWare) external drive
Answer Link: http://wdc.custhelp.com/cgi-bin/wdc.cfg/php/enduser/std_adp.php?p_faqid=3741" ~oxter
https://community.wd.com/t/forgot-password-western-digital-my-passport-external-hard-drive/8283
Since you have the HDD, you can probably keep trying combinations of what you think it might be, but the point of encryption and password protection is to make sure someone can't just get some software to unlock and decrypt the information. Sorry and best of luck trying to remember the password!