Finding duplicate records
It is important to try to avoid duplicates of references in your EndNote Library. Duplicate references in your EndNote Library can lead to repeat references in Bibliographies, which can be tricky to resolve.
To check if your Library has any duplicates, go to References and select Find Duplicates.
EndNote will show you any duplicate references within your library. It is recommended that you delete any unintentional duplicates you find (Note: there may be times when you wish to have a duplicate, for example when your references include different chapters from the same edited book).
After running the EndNote Find Duplicates command it is essential that you follow up with a manual check of your Library for duplicates.
Re-sort your Library Window alphabetically by title (click the Title column heading), then visually scan, identify and delete duplicated records.
Deleting Duplicate Records
Select duplicate records, right click, then select Move References to Trash.
In addition, when importing in PDF files EndNote gives you the option to Import into Duplicates Library (see Importing PDFs).