By default, the project will be built without any bindings to Paint.NET, if you want to enable this build the project for windows and with the feature pdn-sys enabled.
This will build both a vendored version of OpenRasterFileType and the dotnet bridge necessary for the rust side to be able to interface with Paint.NET. Dotnet 9 or higher is required to build them.
These C# projects will be located under ./shared and by default require Paint.NET to be installed in C:\Program Files\Paint.NET (ie the default location for installation), you can change <HintPath> properties located in the project's .csproj if you would like to have it somewhere else.
You might also be required to move libnethost.lib to the project directory, it would be located inside the C:\Program Files\dotnet\packs\packs\Microsoft.NETCore.App.Host.win-ARCHITECTURE\DOTNET_VERSION folder or wherever else you have dotnet installed.