Why does FPDF throw "Some data has already been output, can't send PDF" when used within a Drupal module?

FPDF Error: "Some data has already been output, can't send PDF"

The aforementioned error typically arises when there is extraneous output present before FPDF attempts to generate the PDF document. For proper PDF generation, FPDF requires exclusive control over the output.

Problem:

Attempts to utilize FPDF within a Drupal module result in the error: "Some data has already been output, can't send PDF." This issue does not occur when using FPDF outside of Drupal.

Solution:

To resolve this issue, ensure that absolutely no output, including spaces or line breaks, is present before invoking FPDF. Here's a corrected example:

<?php
$pdf = new FPDF();
$pdf->AddPage();
$pdf->SetFont('Arial','B',16);
$pdf->Cell(40,10,'Hello World!');
$pdf->Output();
?>

Recommendation:

For seamless integration with Drupal, consider utilizing alternative PDF libraries that offer robust compatibility with the platform. Drupal provides a range of PDF-related modules that may meet your specific requirements.

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