Forms data with custom action

Hello, I want a form where once the user presses ‘send’ it posts that info to a custom php file on the server that executes with that form data. Is this easy to do with wordpress? Do you have to install an addon for forms such as, ninja forms? I tried the addon ninja forms but didn’t find any good way to create my action on the send button. I need it to post to my php file when clicking send/apply. Also required field is important to have which is possible with ninja forms. How to set it up with custom check from a php file. Is this possible?