Many researchers who wish to begin using a citation management tool need a way to transition from a collection of PDFs on their computers. The desktop versions of both EndNote and Zotero can assist with this by importing PDFs and extracting citation information from at least some of them.
Zotero is generally more effective at this task. Instructions are given below for importing PDFs using EndNote, Zotero, and a combination of both tools.
This option often results in more PDFs successfully converted to citations than importing to EndNote directly.