Many colleges, universities, and research institutions provide free EndNote licenses to students and faculty. Even older versions like X6 may be available through site licenses. Steps:
Owned by Elsevier, Mendeley is another popular free option.
EndNote is proprietary software owned by Clarivate Analytics. Using a product key that you did not purchase is software piracy. For university students and academic professionals, this can lead to severe consequences, including loss of access to university networks, academic probation, or legal action from the software vendor.