Zotero [zoh-TAIR-oh] is a powerful, easy-to-use research tool that helps you gather, organize, and analyze sources and then share the results of your research. It collects all your research in a single, searchable interface. You can add PDFs, images, audio and video files, snapshots of web pages, and really anything else. Zotero automatically indexes the full-text content of your library, enabling you to find exactly what you're looking for with just a few keystrokes.
See the quick start guide here: https://www.zotero.org/support/quick_start_guide