If you have a article in PDF or articles in a PDF folder on your computer, you can import the article or the PDF folder to your EndNote Library.
Download the PDF if you have not already done so already and save it where you can find it.
In EndNote, open the reference you would like to attach the PDF to and click on the paperclip button.
Locate where you have saved the PDF and open it
It is now attached to the reference and can be searched, highlighted, e-mailed, and so on
Alternatively, you can drag and drop the PDF from your desktop into the open record in EndNote and it will attach itself.