target a custom page using plugin function in wordpress

target a custom page using plugin function in wordpress

i created a custom page named custom_page.php in wordpress and use this as
a page template.
i wanted to create my own functions and only target my custom_page.php.
this function will be installed as a plugin.
what kind of WP HOOKS should i use, for example i have this code below
function your_function() {
if ( is_page_template('custom_page.php') ) {
echo '<p>This is inserted at the bottom</p>';
{
}
add_action('wp_footer', 'your_function');
i want to only execute this code in my custom_page.php footer area.
[EDIT]