IMHO if the link within the presentation is <a href="Fitness_testing_e.pdf" title="Fitness testing" target="_blank">Fitness testing </a> then moodle isnt going to find it, if you changed the link to
URL /moodle/pluginfile.php/26768/mod_resource/content/3/Fitness_testing_e.pdf, then it should. So my suggestion would be to upload the PDFs first, obtain the url link for each, add those links into the presentation and then upload that.