I'm assuming you mean sites like www.ezinearticles.com ? Yes, you must print it word for word unless you have special permission from the author to change it.
You can also look into PLR (private label rights) articles where you get the ability to change the content so you don't have to worry about the duplicate content filter. Usually there is a membership fee but it's worth it if you don't like to write or at least if you need ideas for content.
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