Design Hook for Ninja Forms

I have ninja forms installed, with an upload file ability – all working fine, I can view the file in the directory and the link to the file in the NINJA FORMS > SUBMITTED
I cannot get the file to attach to the email once form is submitted,
I purchased a plugin – dropzone for ninja forms which should have taken care of attaching the uploaded file to the form email but it did not attach or even uploaded the form and I cancelled the purchase.
My thinking is I need to hook a function to the email submit, to attach the form – do not have the know how to do this although I think it is a pretty simple function to write.