All platforms support PDF.js in the web browser. Alternatively:
- On Linux, use either Atril, Evince, Okular, or Zathura.
- On Windows, use either Okular or SumatraPDF.
- On macOS, just use Preview.
- On iOS, use either Quick Look (built-in) or MuPDF.
- On Android, use GrapheneOS PDF Reader.