The death certificate is a certified extract of the information provided on the death registration. The person looking after the estate of the deceased will need to produce the death certificate whenever they are required to provide proof of death—for example, to cancel a driver’s licence or to settle insurance policies. As you've heard, some institutions will require the “original” death certificate or a notarized copy, while others will accept a regular copy. You may wish to order two originals, then have additional “certified true copies” prepared by a notary public or a lawyer if needed.
See our pages on dealing with an estate for more on the legal issues involved when acting as executor of an estate.