How do I enable checkboxes in Word 2016?
On the Home tab, choose the down-arrow next to the Bullets list to open the bullet library, and then choose the checkbox symbol.
Why is my checkbox not working in Word?
You need to have the document locked (protected for filling in forms) for the checkbox to work properly. The shading is because of your Word preferences for shading of fields. You have it set to shade fields when selected or always.