A family of Microsoft word processing software products for creating web, email, and print documents.
It's just an option setting. Click File > Options > Advanced. In the first group (Editing options), check the box for "Use the Insert key to control overtype mode".
If you want a reminder of which mode is active, right-click the status bar at the bottom of the Word window and click "Overtype" to check it. When the insert mode is active, the word 'Insert' appears on the status bar. If you press the Insert key or click the word on the status bar, the mode changes to overtype and the word in the status bar changes to 'Overtype'. Press the Insert key again or click the word again to switch back.