Thanks for the package. I never new of Poppler but thanks to this package I am interested. I found some issues (not sure if you forgot to include an additional class file or if oversight deleting namespace). I was able to get it working by commenting out a few things in HTML class. Here are the lines one by one commenting out where issue (assuming forgot class file).
Fatal error: Class 'Pelago\Emogrifier' not found Html.php on line 88
Fatal error: Class 'TonchikTm\PdfToHtml\Emogrifier' not found in Html.php on line 88
Fatal error: Call to undefined function TonchikTm\PdfToHtml\mime_content_type() in Html.php on line 110