jPDFEditor provides extensive functionality for viewing and comparing PDFs.
Navigating: General navigation tips and tools
Zooming: Zooming in/out of the document
Setting Page Layout: Setting how the pages are displayed
Rotating Page View: Rotating the view of the page
Loupe Tool: Magnify a small region of the page
Pan and Zoom Tool: Display a window with the current location on the document
Invert Colors Mode: Invert colors when displaying PDFs for accessibility
PDF Layers: enable, disable, create, and edit layers.
Side by Side Comparison: Compare two different PDFs next to each other
Overlay Comparison: Compare two different PDFs on top of each other highlighting the differences