I wanted to set the icon for mine Microsoft .NET WPF application, but I only had a *.png file.
With the IconCur.dll plug-in for Paint .NET I converted the *.png to *.ico file.
|Download the IcoCur.dll from [http://www.evanolds.com/pdn.html] and place the IcoCur.dll in the [FileTypes] folder, found in the same location as the PaintDotNet.exe folder. In my case [C:\Program Files\Paint.NET\FileTypes]|
|Open you’re *.png file in Paint .NET|
|Click File > Save As…|
|Save as type: Icons (*ico)|