What is "Passhegen"?
Rashi: This is Arame'ic; it is the tale of the Sefer.
What is the meaning of "Lehinasen Das"?
Rashi: The command of the writing - there will be a decree of the king.
What was "revealed to all the nations"?
Rashi: This matter (to be ready for this day, Adar 13). Vilna Gaon - on this day, they will tell them what to do. Only the Achashdarpanim and Pachos were informed that all the Jews will be killed. If this were revealed to all, the Jews would petition the authorities to show merit to spare them.
Malbim: He sent two letters. (a) The officers received letters sealed with the king's ring. They were not to be opened until Adar 13. No one knew what was written inside. Kingdoms do so nowadays. (b) Open letters said to be ready for war on Adar 13. Then they will open the sealed letters, and know whom to fight. Haman did so (a) so the Jews would not be able to seek help and salvation, or appoint advocates in Beis ha'Melech, and also the king will not know until after it happens 1 . (b) Via this, he was confident that the Jews will not flee to other Medinos 2 or hide themselves. Since they do not know whom to fight, also they must be ready!
Malbim said above (13) that even the king cannot retract from a letter that he sent (8:8)! Perhaps Haman was concerned lest he send a second letter that will save the Jews, like Mordechai later sent. (PF)