Up to 45 PDF files can be attached to each reference in your EndNote library. 

Use the paper clip on the Tabs panel to attach a PDF file to a reference.

A preview of each attached PDF file will then be available as a tab on the Tabs Panel.

Each PDF preview displays a PDF toolbar at the top. Move your cursor over an icon on the toolbar to see text to explain its function.

The first icon displays Open this PDF. Select it to execute the command and to reveal more options for working with the PDF file, for example to add sticky notes and to highlight text. When finished, select the Close this PDF icon, confirm Save and return to the record.