From - How can I link a Checkbox to input fields (multiple)?

By "activated", I'm assuming you mean enabling/disabling a field. 

One technique is to hide/show fields.

Here's an article on hiding and showing fields. 

https://www.pdfscripting.com/public/Hiding-and-Showing-Form-Fields.cfm?sd=40

It includes an example using a checkbox. The exact same technique can be used to enable/disable fields with the "readonly" field property.  Which is a much simpler version of enabling/disabling.

If you want to get fancy. Here's an article on creating a "disabled" appearance.

https://acrobatusers.com/tutorials/js_disabling_fields/

Another simple way to create a disabled appearance is to cover the field(s) with a gray rectangle annotation.

Hi Ayush29966864hyux,

Thank you for reaching out.

If creating the Acrobat Sign, refer to the following help document to set form field conditions: https://helpx.adobe.com/sign/using/form-field-conditions-settings.html. 

For the Acrobat form, refer to the information provided in the following community discussion on a similar topic: https://community.adobe.com/t5/acrobat-discussions/is-there-a-way-to-make-a-text-field-required-if-a-check-box-is-clicked/td-p/9284750. 

Hope the information helps.

Thanks,

Meenakshi