Leanpub books do not have any DRM or Digital Rights Management features. We will also never do anything like "watermarking" books with the customer's personal details, for example.
Frankly, in our opinion authors should just ignore piracy. Peter Armstrong, a Leanpub co-founder, published two books with a traditional publisher, and both were pirated.
There are many reasons we are against DRM. Maybe the most important one is that doing things like watermarking is inherently offensive: it treats 100% of honest customers like they're thieves. People don't like that, for good reasons.
We understand that this is a sensitive issue and that every author has their own position on it. Our position is that piracy is a smaller problem than obscurity. The best thing to do as an author is to just take the effort that you would have spent sending DMCA takedown notices to pirates, and spend that effort instead on writing blog posts excerpting and promoting your book. Chances are this will be a more profitable use of your time.
Our intention is not to trivialize this important issue. When people see their hard work being ripped off it initially makes almost everyone very upset.