Chrome Extensions can be either packed or unpacked.

• Packed extensions are a single file with a .crx extension.
• Unpacked extensions are a directory containing the extension, including a manifest.json file.

To pack an unpacked extension, use the Pack button in chrome://extensions or use Chrome: "chrome.exe --pack-extension=C:\path\to\unpacked\extension --pack-extension-key=C:\myext.pem". To unpack a packed extension, extract the file. You may need to rename the filetype from .crx to .zip for your zip utility to recognize it.

Refer to the Extensions documentation for other ways to do this which are more automation friendly.

Install Extensions with ChromeDriver

Packed (.crx file)

ChromeOptions options = new ChromeOptions();
options.addExtensions(new File("/path/to/extension.crx"));
ChromeDriver driver = new ChromeDriver(options);

Unpacked (directory)

ChromeOptions options = new ChromeOptions();
options.addArguments("load-extension=/path/to/extension");
ChromeDriver driver = new ChromeDriver(options);