Apostille or Certificate of Authentication. When a document is to be used in another country, it may be necessary to have the document authenticated.We can apostille an authorization letter signed and notarized in all 50 U.S. states, District of Columbia, and the U.S. Federal Government (USA Embassy). Are you looking for an example of a New York Apostille? Discover how to write an effective authorization letter for DFA services and the apostille process easily. That person must bring in: • A written and signed authorization letter from you as the requestor (include in the document your name,. Authorization Letter DFA - Free download as Word Doc (.