How to convert PDF to PNG in PHP without using a library such as ImageMagic

Unfortunately, PHP standard modules do not have the ability to convert PDF to PNG.

By the way, the PDF lib and GD you mentioned are not standard PHP modules, but for some reason it seems that they happen to be usable.

I'm not familiar with libraries that only PHP completes, but there seems to be a Ghostscript wrapper library.

• Ghostscript-PHP
  https://github.com/alchemy-fr/Ghostscript-PHP

As you can see in the document on the page above, it looks like ↓.

$transcoder=Ghostscript\Transcoder::create(array(
    'timeout' = > 42,
    'gs.binaries' = > '/opt/local/gs/bin/gs',
), $logger);
$transcoder->toImage(' document.pdf', 'output.jpg');

'gs.binaries'=>'/opt/local/gs/bin/gs', as you may have noticed,
gs must be installed.

PDFlib does not have the ability to image PDF pages.
http://pdflib.jp/product/

Although there is a function to paste images into PDF files, FoxIt is famous for making PDFs into images (effectively viewer functionality) (but PHP is not available).