Basically they want to be sue that you are the person appointed by the court to adminster the estate of your grandmother.
That document means that an estate has been opened for your grandmother and you are the personal representative of the estate.
No, you don't need an attorney - but it would be adviseable for you to retain one to help adminster the estate.
Attorney
19 years legal practitioner: real estate, collections, estate, civil, business, and criminal law