Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
Altarsoft PDF Reader - Altarsoft PDF Reader is a simple to use PDF files management program that allows its users to view PDF files, encrypt the files and even annotate these files as well.
Academia.edu - Academia is a website where you can share papers that are written with other users. You can use a Google or Facebook account to sign in to the website.
eXPert PDF Reader - eXPert PDF Reader is a free to use PDF reader and views for the Windows operating systems.
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
Xodo - Try easy-to-use PDF tools that keep your documents safe. Work with your important files across all platforms and devices with the ultimate all-in-one document solution. Your productivity lives at Xodo!