E-publishing in easily-copied file form

I recently purchased a download of an anthology on lulu.com. A fair price (and actually for charity). So far, so good.

So the download was in the form of a .pdf file. I was happy about this at first, because it's easy to use.

But then I started thinking: if I really like this book, and have ten friends who want the same book, I could simply send a copy of this file to each of them via e-mail; they'd each have exactly the same e-book I have, without an additional penny going to the people who put the book together and presented it for sale.

(I just sent a copy to my secondary e-mail to make sure; easy-peasy.)

I'd never do that -- but it bothers me that there's nothing in practical terms preventing me. What if I e-publish on lulu, and my book attracts a group of "fans" who like it, but don't have any intention of paying for additional copies, and instead just send each other unauthorized copies. I'd have a word-of-mouth success without getting paid for it; I'd have a fanbase consisting of thieves.

Has anybody had that happen, and is there anything that can be done about it?

Thanks for the replies! I think I'll keep working towards being published the old-fashioned way (as long as it's still around).