.epub3 file: how to open it on Windows

2 Windows apps register the .epub3 extension. Install one of them to open the file with a double-click.

• 
  Thorium

  A cross platform desktop reading app, based on the Readium Desktop toolkit

  Open source 3.5.1 ★ 2.9K
• 
  Alexandria

  Minimalistic cross-platform eBook reader

  Open source 0.13.2 ★ 2.7K

Related guide: Change the default app for a file type in Windows