Plagiarism is the copying of documents, thoughts, reasoning from others and allowing these to pass for personal work. When texts are copied from others, they must be provided with a correct acknowledgment.
If an adopted text is provided with a reference to the source, then there is no question of plagiarism. However, the copyright of the original author may have been violated if more than one quote has been copied. When texts are copied from others, it is therefore highly recommended to ask permission from the author.