A Letter of Testamentary is a court-issued document that proves that the person named in the will is the rightful executor. This document is necessary to settle the estate and distribute assets according to the will.The Letter of Testamentary also gives the executor the legal authority to act on behalf of the deceased person's estate. This includes opening a bank account for the estate, selling property, and paying debts.If you are named executor in a will, you must obtain a Letter of Testamentary from the court. The process for doing this varies from state to state but generally involves filing a petition with the court and proving that you are qualified to serve as executor.