Full version history: https://www.sumatrapdfreader.org/docs/Version-history#3.6
Notable highlights:
- improved Command Palette (
Ctrl + K) - improved editing of annotations
- improved scrolling with mouse wheel and touch gestures
- more customizability:
- new commands
- some commands can now take arguments
- improved theming
- many bug fixes
You can download latest version from https://www.sumatrapdfreader.org/download-free-pdf-viewer or Ctrl + K, Check For Updates using command palette.