Laws of the Megillah
19. [The following laws apply to a] congregation that does not have a
Megillah that is completely kosher ("Ein Kashera Ke'dinah): if it is
written on parchment ("klaf") according to halacha, but is missing a few
words in the middle section ("Emtza'ah"), since a complete subject ("Inyan
Shalem") is not missing, one may read from it and recite the required
blessings preceding it; the reader should recite the missing words from
memory, or someone else should [prompt him] by reading them for him quietly
from a Chumash.
However, if there is no Megillah available at all, or it is missing a
complete subject, or there are words missing at the beginning
("Ba'tchilah") or the end ("Ba'sof"), each person should read it to himself
from a Chumash without reciting the blessings.
An individual who has only a Megillah that is not valid ("Pesulah"), should
read from it without the blessings.