Hello Jeferson,
You don't need to edit any file to enable Google reCaptcha. Simply enable the Google reCaptcha plugin from Joomla administrator > Extensions > Plugins. Now, go to Joomla administrator > System > Global Configuration. And select Google reCaptcha as default Captcha.
You can know more about this, follow the below link.
https://docs.joomla.org/J3.x:Google_ReCaptcha
I hope this helps.
Thank You