The PdfHandler extension serves both .png and .jpg images, depending on the extension in the URL path. But on File:⋯.pdf pages the <div class="mw-filepage-resolutioninfo"> thing shows links only in one format, mandated by [[ https://www.mediawiki.org/wiki/Extension:PdfHandler#Configuration | $wgPdfOutputExtension ]] (currently .jpg on Wikimedia servers). The div should be remodelled along the lines of this script. Trying other resolutions is not as helpful as trying another format, especially PNG over JPEG.