Im writting a document that I'm coping and pasting some content from internet (a lot of) and I don't know if im using the same references when copy and pasting (creating duplications). 

How can I know and find if Im creating a lot of recorrent information on my MS Word document?

PS: Im writting a document that already reached 500 pages, it is humanly impossible to use CTRL+F to search for snippets information duplications.