Many .rar files from forums are password-protected. Look at the site where you found the link; the password is often the site's URL.
WinRAR (the official tool) or 7-Zip (free/open-source). Mac/Mobile: Apps like The Unarchiver or PeaZip work well.
Is this for a specific (like an accounting or HR tool)? Do you need help fixing an error related to this file name?
You will need a program to extract the contents.
Knowing the (e.g., "It's for my office accounting software") will help me find the specific resource you need.
