First download your PDF to your device.
In your Endnote library click on the paperclip icon under the item title you want to add the PDF to, then upload your saved PDF.
You can open the PDF within Endnote, just click on the file to open it. You cannot edit or annotate, only read the PDF.
For more help please contact your Academic Librarian: http://libguides.leedsbeckett.ac.uk/contact_us/library_staff