Hi tomcazoom,
it depends on your browser. It seems PDF are open in your browser because you have a PDF viewer, right ? When I click on a PDF on my computer, it is downloaded, never displayed in the browser. That’s why I don’t know if there is something to do.
You can try manually to change the behaviour and tell me if it works or not…
1. First, edit file wordpress/wp-content/plugins/s2member-secure-file-browser/class/psk_s2msfb.class.php
2. Go to line 1228 (or near this one…)
3. Replace line
$li .= '<div class="jftctn"><a href="#" class="link" rel="' . $link . '">' . $display_name . $extended . '</a>';
by
$li .= '<div class="jftctn"><a href="#" class="link" target="_blank" rel="' . $link . '">' . $display_name . $extended . '</a>';
4. Verify that files are opened in a new window now
It will do the trick for all files. If it works, I will tell you how to enable this feature only for pdf files.