The app checks the file attachement cache on launch. If over 100MB, the app automatically clears space - you do not need to do anything and will not be prevented from downloading more files.
Also, if you download a file attachement and then make it a “favorite” by clicking hte heart icon, these file will stay on your iPad and, if you make amny favorites, the app will allow you to go over the 100MB cache.
So, since you are interested in conserving memory on your device, I recommend NOT making records with PDF file attachements favorites in your EndNote iPad app. You can always download any of your PDF file attachments and they will be availble locally very quickly.
I hope this helps.
Jason Rollins, the EndNote team