I noticed that Megillat Esther mentions two types of documents used to proclaim royal edicts.
In Esther 1:22 the term ספרים is used to inform people that every man should be the ruler of his household.
In Esther 3:13 - 14 ספרים as well as פתשגן כתב to announce Haman's decree to destroy the Jewish people. We see these same two items mentioned in Esther 8:10 and 8:13 when Mordechai announced that the Jews have a right to defend themselves.
What is the difference between ספרים and פתשגן כתב in terms of announcing laws, and why was the פתשגן not used to announce the law stated in Chapter 1?