EndNote allows you to import a single PDF file or a folder containing several PDFs and will then attempt to automatically create a reference for the PDF.
Your PDF will now appear as a reference in your EndNote library.
If the PDF does not have a DOI (Digital Object Identifier), EndNote will create a reference containing only the filename of the PDF in the Title field. The PDF will be attached to this reference, and you will need to edit the reference:
PDF handling preferences allow you to automatically import PDFs from a folder on your computer.
EndNote will regularly scan this folder and import the new PDFs you have saved to it and create a record in your EndNote library.