You can probably do it safely, although it has not been tested in the courts. Probably not, although it is frequently done. Plagiarism Plagiarism, sometimes confused with copyright violation, is presenting someone else's work as your own. Such use may or may not also involve copyright violation. For example, to present a Shakespeare sonnet as your own writing is plagiarism, but it is not a copyright violation, since Shakespeare's hundreds of years old works are not protected by copyright, unless there are modern additions such as scholarly commentary.
Plagiarism is more an ethical issue than a legal one, unless fraud is involved.
In an academic setting, of course, claiming someone else's work as your own has serious consequences. Copyright is not the only form of intellectual property protection. For example, while titles are not protected by copyright, they may be protected by trademarks. Ideas may not be protected by copyright, but they may be protected by patents. Citing Sources of Copyrighted Material.