Execute an UDT on button click

[seregarem]

I have a form. When an user clicks on button, UDT must validates captcha and if it's right send a email. If captcha is wrong, it should be shown a message. All this must be done not sending on another page. So, I think, that it can be done calling an UDT on button click. How to make this?

[Dr.CSS]

If you use formbuilder and install the captcha module then you only need to check the use captcha box...