No.. you can't do anything mate. You just can locked it by using .pdf file but people can still copy it (by using tools or just simply rewriting it). I have faced same problem with my ebook too. huhh.. But you are selling it in $20 and you didn't give any information related to your ebook. lol
have you sold any copy of your ebook?? It's because I am still having problems with how to sell it. I just put something there to make the thread.
so you are saying that its just plain text and you didn't mention in your ebook that you are the author and it is copyrighted??
Its quite hard to protect ebook from piracy, this had been a major problem for freelancers that offers ebook.
I think you have only one way if you want to protect your file from theft. You don't submit your idea in any books or internet. So, nobody can know about your idea and they can't copy it. Sorry don't mind. Just wanna to make fun. Ha ha ha .....