Checkmark not defaulting in form fill

I am filling out a fillable form and multiple pages require I use a checkmark to acknowledge the statements. I select Fill& Sign and select the checkmark but when I click into the box it defaults to a text entry box. I would then have to click elsewhere on the form to generate the checkmark, then click and drag it into the box. I have 120 boxes to fill. The odd thing is sometimes it works and I can click a checkmark directly in the box and other days it does this. I'm sure there's a simple answer but I don't know the magic google phrase to unearth it.