webform form

I have a Webform in drupal 7. I want to add a hidden field porgramatically to it, and I would like to set the value of this field per form. I want to achieve all these in a custom submit function. At the moment everything is working, except to set the value. I googled it a lot, tried out hundreds of codes but non of them worked in my case.

Here is my code:

Sziasztok!