Theming of a webform node i would to theme a specific webform page and i achieve this with devel themer help but i find it not logical.
Usually i use ID to specify a template for a page, node or other element.
Then in my case i use the node-419.tpl for my node 419.normal
For my page it's a bit more complicated because this the hierarchical applied template :

page-infos-profil-élève.tpl.php &lt; page-webform.tpl.php &lt; page-node-419.tpl.php &lt; page-node.tpl.php &lt; page.tpl.php


so why a template called page-webform-419.tpl.php doesn't work instead of page-infos-profil-élève.tpl.php ?
Could i do this with php in my template.php file ? if yes how ?

thanks
This depends on your template suggestions.

Open template.php in your theme folder, and look for a function named YOURTHEME_preprocess_page, if it does not exist, create it like:

function YOURTHEMENAME_preprocess_page(&amp;$vars)
{
    debug($vars['theme_hook_suggestions']);
}


And see what suggestions (and in what order) you have.

EDIT: this is a preprocess function I used in a theme of mine, in theme's template.php:

/**
 * Implementation of hook_preprocess_page()
 * @param $vars
 */
function THEMENAME_preprocess_page(&amp;$vars){
    // I like to store templates in different folders inside the theme dir
    foreach($vars['theme_hook_suggestions'] AS $i =&gt; $ths){
        $vars['theme_hook_suggestions'][$i] = 'pages/' . $ths;
    }
}
/**/


In your case, simply do debug($vars, 'preprocess page vars!'); to see what variables you have a dispostion (please note: flush the cache after editing/creating this kind of function, and the output of debug($vars) can be very big!) and then add your template suggestion.

Maybe this can help: theming d7 webforms