10. It is customary in all Jewish communities that one does not read the
Megillah for the congregation from a rolled up scroll (that is, with the
scroll opened only to the page presently being read). Instead it should be
unrolled [completely] and then folded section over section, like a letter
("Iggeres") (1), because [the Megillah] is referred to as " The Purim
Letter" (Esther 9:29)." The people listening to the Megillah do not have to
unroll their own Megillahs.
(1) The Megillah should be unrolled and folded before the reader recites
the blessings preceding the reading, so that there will be no interruption
between the blessings and the reading.