One way to search for plagiarism is to run a part of the text through Google search engine for matches. You can customize your search by adding quotes to the text, this would create a search for the exact text and not related ones Wich search engines normally use. This is good for exposing copy pastes, but would not exactly work for word spinners and paraphrases

There are also some plagiarism tool, but I've personally not used any of them.