For the source text click/tap here: Megillah 18
To download, click/tap here: PDF
In our daf we read:
“It says ‘Zakhor’(Devarim 25:17). Might this be fulfilled in one’s heart? When it says, ‘you shall not forget(Devarim 25:19)- ‘forgetting’ refers to the heart! So what do I learn from [the commandment] to remember? With one’s mouth.”
Clearly, then, the obligation to remember refers to not simply mental recollection, but rather a verbal recitation.
The Gemara does not specify whether one must read Parashat Zakhor from a proper sefer Torah, or merely recite the words.
Both the Rambam (Hilkhot Melakhim 5:5) and the Chinukh (603) make no mention of reading the text specifically from a Torah. The Ramban (Devarim 25:17) also implies that one does not need to read the parasha from a text, but rather to "relate the story to our children..."
However, some Rishonim (see Tosafot, Megilla 17b s.v. kol and Berakhot 13a s.v be-lashon) rule that even on the level of Torah obligation, one must read Parashat Zakhor from a proper Torah scroll.