Foxit Reader - Foxit Reader is a free and light-weight multi-platform PDF document viewer.
Beyond Compare - Beyond Compare allows you to compare files and folders.
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!
WinMerge - WinMerge is an open source differencing and merging tool for Windows.
Evince - Evince is a document viewer for multiple document formats: PDF, Postscript, djvu, tiff, dvi, XPS...
Meld - What is Meld? Meld is a visual diff and merge tool targeted at developers.