EndNote provides two types of import options: importing of saved ".txt" files and importing of data from PDF files. The former usually involves importing data (references) from databases that do not offer the direct import option or importing data from citation & reference management systems, e.g. EndNote, RefWorks, Mendeley or Zotero. The latter option, the PDF import, involves extracting data from PDF files (full text articles) and then creating EndNote references from that data and attaching the PDFs to those references.
PDF Importing Options