You can convert PDF files into Endnote references as long as the PDF has a DOI (Digital Object Identifier) that Endnote can extract.
To import a PDF file:
Open your Endnote library.
Go to File, select Import. Click File to open the Import File dialog.
Click the Choose button to locate and open the needed PDF fileclick OpenImport.
Select PDF from the Import Option list.
Select an option from the Duplicates list:
Import All: Imports all references, including duplicates.
Discard Duplicates: Imports all references except duplicates.
Import into Duplicates Library: Duplicate references are imported into a library called your library name-Dupl.enl
For text Translation option, choose No Translation.
Click Import to import the file to your library.
When performing the import function, EndNote will put the DOI in the DOI field for data extraction. The PDF is then attached and the file name is put in the Title field.
When the import is complete, the new record is stored in the Imported References group, and will include bibliographic information given for the Digital Object Identifier (DOI) mined from the PDF file such as title, author, volume, issue, page, year, and DOI. This is a perfect time to peruse the imported data to make sure it imported as expected.
Note: if the PDF does not have a DOI, Endnote will create a reference containing only the filename of the PDF in the Title field. The PDF will be attached to the reference. You need to manually edit the reference by adding data to the relevant fields.