On the other hand, public domain works are FREE for your use. You can republish them as is, although you might want to make a few changes such as putting in your own information, editing layout and packaging, etc. Or if you want, you can use the public domain work to create your own derivative work.
Note: A derivative work is, according to copyright law, an artistic creation that includes aspects of work previously created and protected. Derivative works of copyright-protected works is prohibited by law, unless a specific permission is acquired by the author/copyright holder. Since commercial use of a work in the public domain is not protected by copyright law, creating a derivative work out of the public domain is commercially legal.
Since you are free to use information/works from the public domain and use them either personally or commercially without restrictions, the possibility of profiting from public domain works is immediate and very real.
Example of Public Domain Works
All copyrighted works that were published before 1923.
That may seem unimportant, until you realize that while today there is a staggering amount of books and other works published and copyrighted each year, when we talk about the public domain we are literally talking about centuries of published work! And most of this is extremely relevant to today’s world.
For example, there are strong niche followings for these areas:
