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PDF to ImageField (https://www.drupal.org/project/pdf_to_imagefield)

- First, add an imagefield on your chosen content type. This is where the
generated images wil be stored.

- Set the allowed fields to 1 if you just want a cover page, or 'unlimited'
if you want all pages to be generated.

- Next add a filefield to your chosen content type and choose 'PDF to Image'
 as the widget. This filefield should be configured to only accept PDF file types.