Dublicated content

[SinaKashani]

I have someone to write new pages for my site.

How do I know the pages she is writing is not duplicated from other other website.

is there any website or software to do this?

What is the best way to check?

Thank you

[Vizergy]

copyscape.com  You will have to do each page individually but it works well.

[GPainter]

As billy said Copyscape is a great option but you can also take sections of the text put it in Google see what comes up. If you can't trust your copy writer they may not be for you then. You can always ask to see previous work when getting some one new and look to see if its also duplicated etc.