Okular - Okular is a universal document viewer based developed by KDE.
Foxit Reader - Foxit Reader is a free and light-weight multi-platform PDF document viewer.
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
PDFZen - The powerful, simple, free online PDF editor for the masses; free yourself from the fax machine!
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!
Atril - Atril is a simple multi-page document viewer. Atril is a fork of Evince.