Problems with Imagick and PHP in Wordpress - php

Question

Hy, i have this function:
function process_pdf( $file ) {
if( $file['type'] === 'application/pdf' ) {
// Get the parent post ID, if there is one
if( isset($_REQUEST['post_id']) ) {
$post_id = $_REQUEST['post_id'];
$filename = $file[ 'name' ];
$filename_wo_extension = basename( $filename, ".pdf" );
$im = new Imagick();
$im->setResolution(300, 300);
$im->setBackgroundColor('white');
$im->readimage( $file[ 'tmp_name' ] );
$im->mergeImageLayers(Imagick::LAYERMETHOD_FLATTEN);
$im->setImageAlphaChannel(Imagick::ALPHACHANNEL_REMOVE);
$im->setCompression(Imagick::COMPRESSION_JPEG);
$im->setCompressionQuality(100);
$pages = $im->getNumberImages();
$attachments_array = array();
// iterate over pages of the pdf file
for($p = 1; $p <= $pages; $p++){
$im->setIteratorIndex( $p - 1 );
$im->setImageFormat('jpeg');
$im->mergeImageLayers(Imagick::LAYERMETHOD_FLATTEN);
$im->setImageAlphaChannel(Imagick::ALPHACHANNEL_REMOVE);
$im->setCompression(Imagick::COMPRESSION_JPEG);
$im->setCompressionQuality(100);
$page_title = get_the_title($post_id);
$filename_neu = $page_title .'_pagina_'. $p .'.jpg';
// upload new image to wordpress
// https://codex.wordpress.org/Function_Reference/wp_insert_attachment
$upload_file = wp_upload_bits($filename_neu, null, $im);
if (!$upload_file['error']) {
$attachment = array(
'post_mime_type' => 'image/jpeg',
'post_title' => preg_replace( '/\.[^.]+$/', '', $filename_neu),
'post_content' => '',
'post_parent' => $post_id,
'post_status' => 'inherit'
);
$attachment_id = wp_insert_attachment( $attachment, $upload_file['file'] );
if (!is_wp_error( $attachment_id )) {
require_once(ABSPATH . "wp-admin" . '/includes/image.php');
$attachment_data = wp_generate_attachment_metadata( $attachment_id, $upload_file['file'] );
wp_update_attachment_metadata( $attachment_id, $attachment_data );
$attachments_array[] = $attachment_id;
}
}
}
// add new images to a gallery (advanced custom fields plugin)
// http://www.advancedcustomfields.com/resources/update_field/
//update_field( 'field_62a736b215b2f', $attachments_array, $post_id );
$im->destroy();
}
}
return $file;
}
add_filter('wp_handle_upload_prefilter', 'process_pdf' );
when i upload PDF file on wordpress all page is converted to JPG and upload in site.
Function work and do what i need, but problem appear when i upload THIS File:
https://easyupload.io/o6hsk3
for understand where is the problem:
i try to compare this file with another;
i upload a big pdf file with more resolution, page.
All work good, but this pdf file not work:(
have any ideea why?