How does a book enter the public domain?
A book, or other copyrightable work, enters the public domain when its copyright lapses or when the copyright owner releases it to the public domain. U.S. Government documents can never be copyrighted in the first place; they are “born” into the public domain. There are certain other exceptional cases: for example, if a substantial number of copies were printed and distributed in the U.S. before March, 1989 without a copyright notice, and the work is of entirely American authorship, or was first published in the United States, the work is in the public domain in the U.S.
