You can highlight, annotate, and write comments in the EndNote PDF reader. This way, you can keep your annotations, highlights and notes right with your citations in one handy location!
*note: this process may take several minutes*
When EndNote attaches a pdf file to a citation, it saves a copy of that pdf to the data library file in a folder labeled PDF.
Depending on where you saved your library, the file path will be something like this: C:\Users\Documents\My EndNote Library.Data\PDF\