Is there any automated way I can detect if a co-author plagiarized before our paper is submitted? My professor, a co-author and I have been working on a paper for more than a year. I was doing the math and simulations, my co-author was responsible for the writing, and my professor was editing the paper. Now editing of the paper is done. Unfortunately, the co-author is no longer available. My professor called me today and told me he has observed that my co-author copied some sentences from the reference papers. So he asked me to check all of the sentences and highlight and rewrite them again if I found that they were copied. He believes that, these days the reviewers are more concerned about the use of similar sentences in the paper. 

So, What should I do? Check all sentences with other papers? This is not possible without using a machine. the paper contains more than 8000 words. Do you know what software I can use to do this?
I am both confused and concerned about the description of your work process:


  I was doing the math and simulations, my co-author was taking the care of writing and my professor was editing the paper.


It seems clear you are making a contribution worthy of authorship, but as for your "co-author" and professor, it is not clear if their contributions are worthy of authorship. the fact that the co-author is unavailable make the situation difficult. High end plagiarism detection software is still not particularly good and I would be hesitant about using any work written by someone who is known to have plagiarised in the past, especially in the absence of drafts to confirm the absence of plagiarism.

The issue with using software like TurnItIn is not its abilitity to detect and parse copied material, but the limitations on its underlying database. Plagiarism detection software generally does not have access to non-open access publications. If your co-author copied from non-open access publications, then the software will likely miss it. A publishers, like elsivier Edith a large amount of pay walled material may add their own publications to their database making it easy for them to catch the plagiarism.

My suggestion would be to rewrite all the material by the co-author. You could either work from his version and maintain his authorship, or if his only contribution was the writing as you say, then rewrite those sections from scratch and drop him from the list of authors.