What is the significance of the error message "Fatal error: Call to undefined function fdf_open()" in PHP and how can it be resolved?

The error message "Fatal error: Call to undefined function fdf_open()" in PHP indicates that the FDF (Forms Data Format) extension is not enabled or installed on the server. To resolve this issue, you need to enable the FDF extension in your PHP configuration file (php.ini) or install it if it's not available.

// Enable the FDF extension in php.ini file
extension=fdf