EasyMerge2pdf is a PHP library for merging Images and PDFs. It uses the excellent merge2pdf command available for OSX, linux, windows.
composer require ronisaha/easy-merge2pdf<?php
require_once 'vendor/autoload.php';
$m = new \EasyMerge2pdf\Merger(['auto' => true]);
or
$m = new \EasyMerge2pdf\Merger(['binary' => '/path/to/merge2pdf']);
$m->addInput('/path/to/input.pdf', '1,3-8,2,1');
try {
$m->merge('/path/to/out.pdf');
} catch (Exception $exception) {
echo $exception->getMessage();
}