Type the code from the image
If you need a basic contact form, Sitefinity’s built in form tools make creating forms and managing responses a breeze. However, sometimes you need to include a form that will send data to somewhere other than your Sitefinity site (for instance, a newsletter subscription list managed by an external source like MailChimp or CreateSend). This can pose a problem since simply adding your form elements between <form></form> tags won’t work. Since <form> tags within <form> tags count as invalid HTML, some browsers will strip out the second set of <form> tags leaving your form ineffective.
Fortunately, there is a clever workaround using iFrames. Instead of adding in your <form> tags directly onto the page, you code your form within a separate HTML document and then add that document into your page as an iFrame! Follow the steps below to easily add an external form to your Sitefinity site.
<iframe src="LINK TO YOUR HTML DOCUMENT"></iframe>