Creating an vCard from form fields

I need to create a vCard (.vcf) that is sent as an attachment with the mail built from Torro Form.
This should not be a big problem, I guess but I don’t know where to start and what and how to extend.

So, some hints for a dummy on where to start would be greatly appreciated.

(I know the structure of the vCard, I only need help in how to extend / customize Torro Forms. Does it go in functions.php of the theme or an additional plugin. Some handholding to start would help a lot)