According to the NY tax website the Document Number is: "For NYS issued licenses and IDs only. This is an 8 -10 digit combination of letters and numbers and is usually on the bottom right hand corner of the front of the license. If the license was issued after January 28, 2014, it will be on the back of your license under the barcode. If the license was issued to someone under the age of 21, the number will be in the middle of the front of the license next to the signature."