Chacham Ovadia Yosef, in his work Chazon Ovadia (Laws of Purim, p. 229), rules that the Megila, like a Torah scroll, requires "Sirtut," the drawing of straight horizontal lines on each page before the writing of the text. A scribe who writes a Torah scroll or Megila must draw these lines and then write the text on the lines. A Torah scroll or Megila written without "Sirtut" is invalid for use for the required reading, even if only a single row of text was written without a line. Furthermore, if the scribe wrote the text of the Torah scroll or Megila and then added the lines underneath the text, the Torah or Megila is nevertheless invalid for use, since the "Sirtut" must be done before the text is written. (Chacham Ovadia discusses this requirement also in his work Yabi'a Omer, vol. 1, Yoreh Dei'a section, 20:10.)
Later in Chazon Ovadia (Laws of Purim, p. 255), Chacham Ovadia addresses the issue of Torah scrolls or Megilot written through "silk screening," a process involving a silk stencil from which the letters of the Torah or Megila are etched. There were Soferim (scribes) who would place such a stencil over the parchment and then pour ink over it, which is a much more efficient and fail-safe method of writing a Torah scroll or Megila than the traditional method of writing the letters by hand. Although one Rabbi allowed preparing Torah scrolls and Megilot in this fashion, Chacham Ovadia rules unequivocally that such scrolls are invalid for use. One who reads from such a scroll or hears a reading from such a scroll has not fulfilled his obligation, and a Beracha recited over such a Torah scroll or Megila is considered a "Beracha Le'vatala" (a "wasted Beracha"). Chacham Ovadia goes so far as to say that a person who sells or purchases a Torah scroll or Megila prepared in this fashion commits a sin for which he will be held accountable before the Heavenly Tribunal.
It is generally very difficult to distinguish between a Torah scroll or Megila prepared through "silk screening" and one that has been written properly. One who purchases a Torah or Megila must therefore ensure to purchase it from a reliable, God-fearing Sofer (scribe) whom can be trusted to prepare the Torah or Megila in accordance with Halacha.
Summary: A Sofer (scribe) writing a Torah scroll or Megilat Ester must first draw horizontal lines on each page before writing the text, and then write the text on these lines; otherwise, the Torah or Megila is invalid for use. A Torah scroll or Megila that was prepared by pouring ink over a stencil placed on the parchment is invalid for use, and one must therefore ensure to purchase Torah scrolls and Megilot from a trustworthy and God-fearing Sofer.
