I have use this code to convert PDF file to JPEG images
$im = new Imagick();
$im->setResolution(90,90);
$im->readImage($pdf_file);
$im->setImageFormat('jpeg');
$im->writeImages($save_to,false);
$im->clear();
$im->destroy();
and it work but I have a problem that when there is a text with white background it will not be clear but I don't have this problem when ever I have colored BG.
this image will make every thing clear