I have been a user of EndNote since version 2. I recently upgraded from 14 to 16 and was disappointed with the new PDF viewer. Inserting PDFs was a great innovation but the annotation tools for the PDF files in version 16 leave much to be desired and the PDF viewer is difficult to use. Here are the problems:
To read the PDFs you need to enlarge the EndNote window to the point that it interferes with the other windows on the desktop and prevents effective use of the other software. If you open the PDF in Adobe Reader or Adobe Professional instead, you can move the window and/or resize it as needed which gives greater flexibility.
The annotation tools for PDFs in EndNote are very limited compared to Adobe Reader or Adobe Professional which reduces functionality. It also appears to be impossible to switch off the internal Adobe viewer.
If one uses Adobe to view and annotate PDF files, they cannot be saved back into to the EndNote data folders. Presumably, this is because the PDF is already open in EndNote. One has to go through a cumbersome process of saving the annotated file from Adobe and then replacing the original in the EndNote record. Version 14 allowed direct save of annotated files into the library.
I have given up on Version 16 and will go back to 14.
KRS