Copyright protection has a legally-defined time period that varies depending on the type of work and who created it. When that time ends, the copyright protection ends and works then belong to the public. At that point anyone

How long does it take for a work to become Public Domain?

Works typically become public domain 70 years after the death of the author or creator, but there are other factors which come into play.

What about new editions of works from the Public Domain?

There are many instances where old works have been reedited and republished, so while the text itself may be free of protection, the edited and republished copy held is still under protection and cannot be copied without permission or payment of royalties.

To be clear, the copy "in-hand" must have expired protection for you to use it freely.