This extension will create thumbnails of PDF files much as DJVU is.

default values are:

$wgMediaHandlers['application/pdf'] = ‘PdfHandler’;
$wgPDFThumbType = array(‘jpg’, ‘image/jpg’);
$wgPDFConverters = array(‘ImageMagick’ => ‘$path/convert -background white -thumbnail $widthx$height\! $input[0] JPG:$output’);
$wgPDFConverter = ‘ImageMagick’;
$wgPDFConverterPath = ”;
$wgPDFMaxSize = 2048;
$wgPDFDPI = 300;

As you can see the default thumbnail type is jpg. If you wish to use ‘png’ or ‘gif’ replace ‘jpg’ in $wgPDFThumbType and $wgPDFConverters.