There are two options:
- Wrap your form into your site using the "wrapper" menu option.
- Re-create your form with a joomla form component.
Option 1. Is ok, it keeps the existing layout, but you don't get any validation rules or advanced options like storing the results in the database.
Option 2. Is the best option but if its a large form be prepared for it to take you a while to recreate all the fields and you have to re-create the existing layout from scratch.
So how do you import an existing form into joomla?
bfForms has the answer in a hidden feature!
Don't ask why it's hidden I've been moaning at Phil Taylor to make it more obvious for a very long time. But once you've found it, and I'm spilling the beans here, you will be importing html forms directly into bfForm in seconds. Once the form is imported all you have to do is add any validation rules you require and the on-submit actions.
It's so easy to do you will be wondering why no one thought of it before.
It's actually quite hard for me to explain how to do this. Not hard to do just hard to explain. So to make it easier just watch this short walkthrough movie.