As I mentioned in the comments, you should not and also can not use codes inside your content. Any code tags that you use will be escaped.
Instead, define a shortcode in your theme's functions.php
file and use that inside your content. Let's create a simple shortcode together:
function create_shortcode( $atts ) {
// Create a default value for the attributes
$atts = shortcode_atts(
array(
'parameter' => 'default value',
),
$atts,
'my-shortcode'
);
// Add your functions here and return the value.
// The value can be anything, including a full
// HTML code or a form.
return "value = {$atts['paremeter']}";
}
add_shortcode( 'my-shortcode', 'create_shortcode' );
Now, by using [my-shortcode parameter="sample"]
in your content you can output value = sample
. Replace the code inside the shortcode with whatever you desire, which in your case is a HTML form.