Public domain is material or work that the public can use anyway they want. People explore, edit, reproduce and sell these works and they gain unpredictable financial benefits out of this.
It’s not so simple, people spend time to dig in the information and find the work that is relevant to today’s scenario, the work which can never become obsolete. They edit, reproduce the work and get the financial benefits out of this work.

One can use this information or work to create e-books, manuals, articles or reports. The good part is there are hardly few people who know about Public Domain Content and the way they can make monetary benefits out of it. First we must understand a few things here:
Work on the internet that is free to use is not all in public domain
Public domain work on the internet is not all obsolete. There are creations which can never become obsolete.

Where can one find this work: The work which you find in the bookstores are mostly edited and reproduced and is normally protected by some law. But the original work of the same author can be borrowed from a library or museum and reproduced at no cost.

The works which can never become obsolete are literature, art, sculptures, music, story books and several health related books.

People spent time and money and reproduce this work. Some people sell this work and some give it as freebies along with their main product. Here is an example of a guy – he bought a book on fitness from a second hand book store for almost free. He edited, reproduced the book, made videos from the book and in today’s date this is the only work he is doing. He earns a whooping $200000+ ever year from this work.

Here is another example – Many yoga (Fitness regime from ancient India) books that we find in the stores for $ 45 – 50 are mostly copied from the books that were written hundreds of years ago. All that these people do is find these books from the libraries and translate it from Sanskrit (One of the most ancient languages – associated with Aryans) to other languages, add photographs of the steps, make fancy covers, gives a few interviews in the newspaper. This little effort makes the generations’ old book resell like a cash cow. This doesn’t mean that every book that was written years ago will generate good revenues. If topics are not chosen carefully it might give disastrous results.

Some people learn the ancient arts (Feng-shui, Vaastu-Shastra) using public domain content and become active consultants for these ancient sciences which are very much in demand around the globe.

Most of the works done by the governments also come under public domain. People collect the reports – prepare summaries and sell it to different organizations and scholars who might need the same to view different aspects of economy.

One can imagine that all they need to do is identify the work, polish it and reproduce it to the public in a more presentable form. It’s not too difficult for a normal human brain to generate ideas and cash on it.