Having published various works I had to look very closely at copyright law in regard to quoting and sought advice from a publisher. All writing is automatically copyrighted and the property of the author. An entire work cannot be posted, but a small portion of an entire work can be posted provided the author is credited. Quoting others work is permissible under the defence of ‘fair use.’
Paraphrasing in ones own style is permissible because copyright seeks to protect the authors style not the actual information. Once someone publicly shows their work they cannot use privacy laws to stop others disusing, quoting or commenting on what has been made public. If this were not the case the Watchtower Society would sue everyone who quoted their past failed prophecies. No author would be able to use a single reference, and encyclopaedias would not exist.