How can the file path for the font definition file in FPDF be correctly specified in PHP to avoid errors?

When specifying the file path for the font definition file in FPDF in PHP, it is important to use the correct server file path to avoid errors. To ensure the correct file path is used, it is recommended to use the `$_SERVER['DOCUMENT_ROOT']` variable to get the root directory of the server and concatenate it with the relative path to the font definition file.

// Specify the file path for the font definition file
$font_path = $_SERVER['DOCUMENT_ROOT'] . '/path/to/font/directory/';

// Include the font definition file
require($font_path . 'helvetica.php');