15. A person who has a Megillah scroll which is not kosher ("Pasul") or a
printed text ("Chumash") of the Megillah, in front of him [during the
Megillah reading], should not read along with the reader, because if he
did, it would be difficult for him to concentrate on hearing what the
reader is reciting. Furthermore, even if he [himself] can concentrate,
another person might hear him reading and focus on it rather than
concentrating on the reader. Similarily, no one should assist the reader by
memory. By the same token, the four verses of redemption (1) which the
congregation customarily recites aloud, should be repeated by the reader
from a kosher Megillah (2).
(2) In order to fulfill the obligation, one must read the Megillah, or hear
it being read from a kosher scroll. One who recites the words of the
Megillah from memory or hears someone recite it from memory, has not
fulfilled his obligation.