DISCLAIMER: the following is my personal belief, and I don't have more than a few anecdotes to back it up.

You shouldn't be concerned about copying no matter the format. Almost anyone who gets a copy of your book illegally is someone who would not have read your book at all if he couldn't have gotten it for free. And with these people, you are better of if they do get it; they may share it with someone who will become a customer, or they themselves may become customers in the future, when they learn that they like what you do and/or their purchasing habits change.

Gumroad has a feature called PDF stamping [1] that puts the buyer's email address on the PDF. It's not perfect security, anyone who wants to ignore your copy rights probably will, but it might deter unthoughtful sharing.

Also consider a team/company license priced at some multiple (15x?) that will allow a manager or lead to buy your book for their company/team without having to worry about violating copyrights or managing buying the book for every employee.

[1] - http://blog.gumroad.com/post/40614820182/introducing-pdf-sta...

Also look to localize. Some countries actually value purchasing a book over the software referenced (e.g. China) and you can make more $ that way.

Will you consider publishing the epub version on leanpub [1] as well?

For some reason, iBook store does not allow purchase from my country. It's been like this for years now. Ditto with Amazon.

[1] - https://leanpub.com/authors

I hope the pdf version of this book will be available. I just don't know how to read Kindle e-book on Linux.