What is the FPDF error "Could not include font definition file" and how can it be resolved in PHP?

The FPDF error "Could not include font definition file" occurs when the font definition file specified in the FPDF library is not found or included correctly. To resolve this issue, you need to make sure that the font definition file is located in the correct directory and is included properly in your PHP script.

// Include the FPDF library
require('fpdf.php');

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

// Create a new FPDF instance
$pdf = new FPDF();

// Add a page to the PDF
$pdf->AddPage();

// Set the font for the PDF
$pdf->SetFont('Helvetica', '', 12);

// Output the PDF
$pdf->Output();