creating conditional fields (displayed if conditions are met)

Hi! Good news — you can do this in Acrobat Pro itself, with no third-party tool and no Acrobat Sign needed.

The simple version (one controlling check box):

1. In Prepare a form, select the field/text that should appear conditionally, open its Properties > General, and set it to Hidden.

2. Select the check box that will control it, open Properties > Actions, choose trigger Mouse Up and action Show/hide a field, then set it to Show that field.

It doesn't matter that the check box is a couple of pages later — the action works across pages.

For your case (shown if one OR several check boxes are ticked), use a tiny JavaScript instead, because separate Show/Hide actions would hide the field again when you untick just one box. Add this as a Mouse Up > Run a JavaScript action on each controlling check box (replace the names with your own field names):

var show = this.getField("Check Box1").value !== "Off" || this.getField("Check Box2").value !== "Off";

this.getField("ConditionalField").display = show ? display.visible : display.hidden;

Acrobat documents both action types here: https://helpx.adobe.com/acrobat/desktop/work-with-pdf-forms/customize-form-fields/field-settings.html

Hope that helps!