You'd first have to wait for the RAR file to upload and then wait for the converted file to download, something that might take quite a while for a really large file.
If you're converting a large RAR file, I recommend using a free tool like IZArc.
If the above program isn't able to unlock your RAR file, you should give Free RAR Password Recovery a try.
It uses brute force to make guessing attempts at the password.
File sharing websites and software distributors sometimes put their files in a RAR file so that they can compress it down to a smaller size, allowing you to download it faster than you otherwise could.
Apart from just saving on download time, RAR files can also be protected with a password and encrypted so that the contents inside of them stay hidden unless you know the password.
Before you run off and buy it, however, you should know that there are plenty of free RAR openers that can do the exact same thing but at zero cost. Once installed, you should set it up to automatically associate itself with RAR files so that, going forward, you'll be able to just double-click or double-tap a RAR file anywhere on your computer and it'll open automatically in 7-Zip. From the Tools menu in 7-Zip, choose Options..., and then select rar in the list of file types.
Then click on the Plus button for either the current user or all users (or both).
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