Zotero is a free to download & use, open source citation manager.
Features:
♦ capacity to retrieve publication data from websites, journal articles, and newspapers,
♦ automatically downloads publication data for imported pdfs,
♦ Word processor integration for MS Word, Libre Office, and Google Docs,
♦ Automatically adds publication data to reference by DOI or ISBN,
♦ Can locate open access versions of paywalled content,
Zotero runs from your desktop. Download it free from https://www.zotero.org/download/
Access Zotero's complete Quick Start Guide