electron/docs/tutorial/using-pepper-flash-plugin.md

Using Pepper Flash Plugin

Electron now supports the Pepper Flash plugin. To use the Pepper Flash plugin in Electron, you should manually specify the location of the Pepper Flash plugin and then enable it in your application.

Prepare a Copy of Flash Plugin

On OS X and Linux, the details of the Pepper Flash plugin can be found by navigating to chrome://plugins in the Chrome browser. Its location and version are useful for Electron's Pepper Flash support. You can also copy it to another location.

Attention: On windows, Pepper Flash plugin is win32 and it won't work with Electron x64 version.
Get win32 version from Electron Releases

Add Electron Switch

You can directly add --ppapi-flash-path and ppapi-flash-version to the Electron command line or by using the app.commandLine.appendSwitch method before the app ready event. Also, add the plugins switch of browser-window. For example:

// Specify flash path.
// On Windows, it might be /path/to/pepflashplayer.dll or just pepflashplayer.dll if it resides main.js
// On OS X, /path/to/PepperFlashPlayer.plugin
// On Linux, /path/to/libpepflashplayer.so
app.commandLine.appendSwitch('ppapi-flash-path', '/path/to/libpepflashplayer.so');

// Optional: Specify flash version, for example, v17.0.0.169
app.commandLine.appendSwitch('ppapi-flash-version', '17.0.0.169');

app.on('ready', function() {
  mainWindow = new BrowserWindow({
    'width': 800,
    'height': 600,
    // web-preferences is deprecated. Use webPreferences instead.
    'webPreferences': {
      'plugins': true
    }
  });
  mainWindow.loadURL('file://' + __dirname + '/index.html');
  // Something else
});

Attention: You can check if Flash dll was loaded by running navigator.plugins on the Console (although you can't know if the plugin's path is correct)

Enable Flash Plugin in a <webview> Tag

Add plugins attribute to <webview> tag.

<webview src="http://www.adobe.com/software/flash/about/" plugins></webview>