Auto increamented field in webforms
Create a custom module and alter the fields value using hook_form_alter()

&lt;?php

function pahcom_form_edit_module_form_alter(&amp;$form, &amp;$form_state, $form_id) {
    if($form_id =='formid) {
        $new_value = rand(100000,10000000);
        $form['submitted']['vendor_id']['#default_value']=$new_value;
        //$form['submitted']['vendor_id']['&lt;h&lt;/h4&gt;default_value']=$new_value;
    }
}

?&gt;