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.
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
eXPert PDF Reader - eXPert PDF Reader is a free to use PDF reader and views for the Windows operating systems.
Qiqqa - Qiqqa is a free research and reference management software. It can be used in many organizational projects from the academic to the personal to the business endeavor. Read more about Qiqqa.
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!
JabRef - Graphical Java application for managing bibtex (. bib) databases.JabRef · JabRef Help · JabRef | Blog · OpenOffice/LibreOffice .