If you have two or more EndNote libraries and want to merge them into one single library, there are three ways to do it: you can copy references from one library to another, you can drag-and-drop references from one library to the other, and you can import one library into another. Below these three ways are described.
Please note that whenever a reference is copied from one library to another the record number of that reference changes. This means that if you have a paper (Word document) with references from the earlier library, they will no longer be in concordance with the same references in the new library since they have got different record numbers. If you want to retain the connection between those references in the Word document and the new EndNote library, they have to be exchanged with the references from the new library.
You should also consider deleting any duplicate references in your library.
You can copy references from one library to another in either of the following two ways:
Import one library into another
Import File: Click on Choose to find the library you want to copy from your computer.
Import Option: Select EndNote Library from the drop-down menu.
Import All - imports all references, including duplicates
Discard Duplicates - discards all duplicates when importing references
Import Into Duplicates Library - duplicate references are imported into a file called File-Dupl.enl, where "File" is the name of the library into which you are importing (e.g. CAST-Dupl.enl)
Text translation: Set this to No Translation.