How do I protect my font against illegal uses of my fonts once I am done creating them? What if I take an existing font and change it? is that against the law? How do I know what is legal and not legal?
Realistically, you can’t. In Europe you can get more protection legally than you can in the US but it’s a waste of money unless you are a big corporation that can subsidize it.
The bottom line on font piracy is, don’t lose a lot of sleep over it. Experience in many instances has shown that you really can’t do much about it. It’s going to happen.
Whatever you do, don’t take an existing commercial font and change it then call it your own work. If the original rights owner chooses to do so, you will wind up in court for your trouble.
Roughly, by definition:
Legal == Draw and digitize your own design or a revival of a much older design – completely from scratch.
Not Legal == Just about everything else.
Some of these questions are not about the law, but about the terms of the licensing. Look into End User License Agreements (EULAs). For example, there should be one associated with whatever existing font you’re thinking of altering, that spells out what is allowable and what is not.