PHP file submission form to be integrated into new Bootstrap site

I have a functioning PHP form which emails the contents of the form along with up to four attachments, the functioning page exists on an old website which I am replacing with a Bootstrap site instead. The Bootstrap site has a contact form on it already, I want this form to inherit the PHP form of my old site, giving the same functionality of my old site but with the appearance of the more modern Bootstrap site instead. The Bootstrap contact form currently has fewer text fields than my old form and there is currently no function to add attachments, as the old form does. The new form should render well on a mobile, as the current Bootstrap form does. The old form has security measures in place to ensure it cannot be exploited by bots, this feature should also be carried over to the new form. This is a simple enough job for someone with the right skills :)