Is it permissible for someone who has not memorized the Istikhara supplication to read it from a paper?

It is not a condition to memorize the supplication for Istikhara (guidance prayer); rather, it is permissible to read it from a paper or a book. However, it is better if one can easily recall it by heart. The majority of scholars have permitted reading the Qur'an from the Mushaf (physical copy) during prayer.