A death certificate or Certificate of Death was an official report that documented the death of an individual. They could be invaluable sources of information when performing genealogical research. (VOY: "11:59")
The death certificate viewed in "The Next Phase" was a modification of the personnel file viewed in "Conundrum". When Crusher certified Ro's death in the personnel file, she changed her Current Status to "Deceased" and added the date of death.