ADE 4.5 hang-up

I just downloaded a book to ADE 4.5 on my MacBook Air OS 10.11.5 and highlighted a number of things in the first ten pages of it before going to bed. When I returned to it this morning, I continued my way through the chapter. But now as I attempt to make my way back through my notes to review, it seems that scrolling through the text has become all but impossible. The app is not showing as "not responding" in Force Quit, but it is so slow as to be useless. I have restarted it several times and it clears up sometimes momentarily, but the longest I have been able to get it to work is about an hour. Any suggestions?