Please help! How so I set up a fillable pdf so that checking one box, opens up a signature field?

To achieve this in a fillable PDF, you'll need to use JavaScript. Here's a step-by-step guide on how to accomplish it:

1. Open your PDF form in Adobe Acrobat Pro.

2. Select the radio button field that allows users to select one of the two options.

3. Go to the "Properties" panel for the selected radio button field.

4. In the "Options" tab, make sure each radio button option has a unique name (e.g., "Option1" and "Option2").

5. Go to the "Actions" tab and select "Mouse Up" as the trigger.

6. Click the "Add" button to create a new action.

7. Choose "Run a JavaScript" as the action.

8. In the JavaScript editor, enter the following code:

Replace "Option1" with the name of the first radio button option and "SignatureBox" with the name of your signature field.

1. Click "OK" to save the action.

2. Save your PDF form.

Now, when the user selects the first radio button option, the signature box should appear, and it should disappear when the second option is selected.

Remember to test your PDF form to ensure that it behaves as expected.

As Mouse UP action of checkbox, use this:

if(event.target.value != "Off")
this.getField("Signature1").display = display.visible;

If you need something more complex to hide a field if the checkbox is unchecked, you can use calculate script in any text field (in that case remove the above script if you added it)

var check = this.getField("Check Box1").value;
var sig = this.getField("Signature1");
sig.display = (check == "Off") ? display.hidden : display.visible;

Change "Check Box1" to your actual name of checkbox that will show/hide signature field.

Change "Signature1" to your actual name of the signature field.

In case you have mutually exclusive checkboxes:

let's say export value of the checkbox that control signature field display is "Yes", in the calculation script

change: == "Off"

to: != "Yes"