A notarised copy officially confirms that the document in question is in fact a copy of the original document. You can request such notarised copies from a notary, but also from public institutions and churches, as well as from the institution which issued the original document. You will need to provide both the original document and the copy to the notary/official, who will then officially stamp and sign the copy. The official notarised copy should now be added to your application documents.