Split PDF to individual pages using FPDI and FPDF while keeping the original PDF's size

gistfile1.php

<?php

/**
 * Split PDF file
 *
 * <p>Split all of the pages from a larger PDF files into
 * single-page PDF files.</p>
 *
 * @package FPDF required http://www.fpdf.org/
 * @package FPDI required http://www.setasign.de/products/pdf-php-solutions/fpdi/
 * @param string $filename The filename of the PDF to split
 * @param string $end_directory The end directory for split PDF (original PDF's directory by default)
 * @return void
 */

/*composer.json

{
    "require": {
        "setasign/fpdi": ">1",
        "setasign/fpdf": ">1"
    }
}

*/

require_once('vendor/autoload.php');
use \setasign\Fpdi\Fpdi as FPDI;

function split_pdf($filename, $end_directory = false)
{


	$end_directory = $end_directory ? $end_directory : './';
	$new_path = preg_replace('/[\/]+/', '/', $end_directory.'/'.substr($filename, 0, strrpos($filename, '/')));

	if (!is_dir($new_path))
	{
		// Will make directories under end directory that don't exist
		// Provided that end directory exists and has the right permissions
		mkdir($new_path, 0777, true);
	}

	$pdf = new FPDI();
	$pagecount = $pdf->setSourceFile($filename); // How many pages?
	$pdf->close();

	// Split each page into a new PDF
	for ($i = 1; $i <= $pagecount; $i++) {
		$new_pdf = new FPDI();
		$new_pdf->setSourceFile($filename);
		$tplIdx = $new_pdf->importPage($i);
		$size = $new_pdf->getTemplateSize($tplIdx);
		$new_pdf->AddPage();
		$new_pdf->useTemplate($tplIdx,null, null, $size['width'], $size['height'], TRUE);

		try {
			$new_filename = $end_directory.str_replace('.pdf', '', $filename).'_'.$i.".pdf";
			$new_pdf->Output($new_filename, "F");
			echo "Page ".$i." split into ".$new_filename."<br />\n";
		} catch (Exception $e) {
			echo 'Caught exception: ',  $e->getMessage(), "\n";
		}
		$new_pdf->close();
	}
}

// Create and check permissions on end directory!
split_pdf('filename.pdf', 'split/');

?>

if your PDF version is >1.4, then use ghostscript to change the version to 1.4

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dNOPAUSE -dQUIET -dBATCH -sOutputFile=NEW_FILENAME.pdf ORIGINAL_FILENAME.pdf

https://stackoverflow.com/a/22430830/2953835