add pdf file download if available
add pdf file download if available

caneruguz/ember-preprints,baylee-d/ember-preprints,baylee-d/ember-preprints,CenterForOpenScience/ember-preprints,laurenrevere/ember-preprints,caneruguz/ember-preprints,laurenrevere/ember-preprints,CenterForOpenScience/ember-preprints