In PDF, you usually need a tick or cross to mark the selection status.
Choice is the proper widget to fit in. There are two kinds of choice, one is
Checkbox which allows multiple selections, the other
Radio Button allows only one selection. From its properties dialogue, you can turn on/off
Multiple Choices option to switch between easily.
Add Choice to add more items, each item has a draggable square widget in the right side PDF panel, drag it to the proper location in your PDF. In the web form, each choice item has the different label to tell what this option is for. Once it is selected in web form, a tick or cross is rendered into your PDF with the location you dragged.
Other Choice option, you can add a text box in web form which is rendered as text in your PDF.