Re-sell, Re-distribute, and Reap Public Domain Profits
One of the easiest ways to earn money from public domain e-books, duplicating the exact content of public domain works and re-selling them can be a great way to start your business. You essentially do not have to spend a lot on material.
Since the product is already in the public domain, there are no royalties and no worries about copyright infringement. You do not even have to get permission from the original author in order to excerpt, reprint, or advertise their products.
You can make as many copies as you want of the original public domain work, convert them into downloadable e-book format (See previous section for instructions on how to create an e-book) and you would be all set to start re-selling, re-distributing, and reaping in the profits.
All in all, it sure is one easy way of earning money, literally without spending a cent.