Extract PDF front page and store it as an image field in node
Oh I just realized that another module, the PDF to Image Field module does exactly what I need! Some more details about thsi module (from its project page):

The PDF To ImageField module provides automatic conversion of uploaded PDF files to images. It can be used either to create a snapshot of the front page to use as a preview thumbnail, or to generate a gallery of images from each page in the document.
The module is implemented as an additional widget for File Field where PDFs are uploaded to. It places generated images into a Image Field on the same content type.

At least, I hope this helps other people too.