You can import a folder of PDFs that will be put automatically into a Group named with the folder name.
Choose File > Import and click Options in the bottom left of the window
Under Import Options, choose PDF Folder as a Group Set > Import
Import PDFs automatically
You can import PDFs automatically from a default folder on your computer.
Set up a folder on your computer and save PDF documents in this folder
Open your EndNote, go to EndNote X8 > Preferences > PDF Handing
Tick Enable automatic importing, navigate to your default folder and click Open > Save
Any new PDFs added into this folder will be automatically imported into your EndNote library when you next open EndNote. References will be created (as long as the PDFs have a DOI) and the PDFs will be attached.