If you meant a different plugin or a specific feature within it (like "feather outline" or "gradient outline"), let me know and I can clarify further.

Adjust the Width and Softness sliders. You will see a real-time preview on your canvas. Finalize: Click OK to apply the border. Where to Get It

As Paint.NET does not have an automated plugin store, installation is manual.

The "Outline Plugin" category refers to effects that generate a stroke around the opaque pixels of the active layer.

If downloading the DLL manually, move it to your Paint.NET installation folder (usually C:\Program Files\paint.net\Effects ).

Outline Selection - Plugins - Publishing ONLY! - Paint.NET Forum