Duplicate content is something which needs addressing as Google can sometimes see this as an attempt to manipulate search engine rankings in an attempt to win more traffic for internet marketing purposes. When content is deliberately duplicated then Google could remove your site entirely from the Google index and thus you will no longer appear within the search results.
This is a highly deceptive practice and in most causes it results in annoyance for visitors to your site when they have to crawl through the same content repeated over and over within a set of search results. In regards to Google search then they will try hard to index and show pages which hold distinct information which is unique.
When Google crawls your site and finds content that is duplicated in order to enhance that sites rankings then they do act upon it. As mentioned they will make the appropriate adjustments to their indexing and ranking of your site and the others involved. As a result your site could drop from top positioning too much lower or even worse it could be completely removed from the search engine results completely.
Many people would get around this problem by blocking crawler access to duplicated content on your website however, this is not recommended. In the majority of cases many people believe that they will get away with duplicated content or content where just a few words have been changed as this is not grounds for action.
The problem arises when you get caught out and reported to Google for deceptive practices and your site is removed from their indexing. In order to get your site back within the Google following this removal then you need to make changes to your site so that it no longer violates the Google guidelines and then you need to fill out a form and submit your site for reconsideration.
Sometimes if content from your site is being copied and pasted into another site resulting in duplicated content then you may well be removed from the search index results. This obviously isn’t your fault but if you do believe another site to be duplicating your content then they are violating copyright law you can contact the site host to request removal and if this doesn’t work then you can have Google remove the infringing page from the search resulting by filling a request.
If you do find an article that you would like to feature on your site then rather than copy and pasting it directly, maybe changing a few names here and there and forming duplicate content you should re-word the article into your own words completely.