One might get away with rewriting the content and not copying it word-to-word. However, it’s unethical and is referred to as stealing. If you are giving an idea that has been taken from some source but presented in an entirely different way, so that no one can recognize it, you are still morally answerable. It is mostly done in the name of research; students mention that as a result of the research, they have proposed something, while that proposition is not what they think about the topic.
On the other hand, it’s copying when you are using other people’s ideas and are interpreting them in your own words.
The original authors should be credited for the work they have done. Even if you are not copying the content exactly, you should be careful about giving them the credit they deserve by citing references.
I would like to mention here that intentions play a major role in whether you are stealing someone’s work or are dog justice to the author while quoting him/her. If one is not stealing an idea intentionally, there is least to worry about. But when you use your own style to present another person’s idea as your own, you are surely stealing and can be held accused of it. Moreover, this is when plagiarism becomes theft.