A copy will be acceptable.
The IRS provides the following guidance on the matter, taken from IRS Pub. 559 Survivors,
Executors, and Administrators:
"If you are the personal representative and the return is not a joint return filed with the decedent's surviving spouse, file the return and attach a copy of the certificate that shows your appointment by the court. (A power of attorney or a copy of the decedent's will is not acceptable evidence of your appointment as the personal representative.) If you are filing an amended return, attach Form 1310 and a copy of the certificate of appointment (or, if you have already sent the certificate of appointment to IRS, write “Certificate Previously Filed” at the bottom of Form 1310)." [Emphasis added.]