Aspire E 14 E5-473G-304W Microsoft office product activation key

Earlier Toady I just Bought This Acer Aspire E 14 from trinoma.
and im trying to activate the microsoft office but its asking for product activation key?
is the Microsft office here is for trial only? if yes, how do i start the trial? What should i do for me to be able to use the MS word and excel?
and thus, do i have to purchase it afterwards?
Please help me. Thanks in advance.