Call function in wysiwyg editor

Hi there,

I’m currently writing my first plugin.

I finished most of the functions and now I want my other admins to be able to call one of the functions in the wysiwyg-editor when creating a new page.

Something similar to {event_description} in the WP-events calendar that shows the description of that particular event.

The function shows a form, sends an email and calls to another function (to create a PDF as an attachment for the email).

Could anyone help me with this?

The function looks like this:

function kna_user_contents(){
    include('plugins/knakaartenapp/kna_user_pagina.php');
}

Kind regards,

Niels