Usage patterns
正式に〈動詞〉to formally do something
The two of them are going to formally get married next month.
正式な〈場所〉an official/formal occasion or setting
Those clothes don't quite suit a more formal occasion.
〈相手〉と正式に契約するto formally sign a contract with someone
The company formally signed a contract with the new business partner.
正式に認めるto officially acknowledge/recognize something
The organization was officially recognized by the government.
正式な手続きを取るto go through the proper/official procedure
You need to go through the proper procedures to study abroad.