The easiest work around would be to simply open your source file in notepad or any text editor, then start a new project in the current AGK-IDE with the name of your project. A folder with your project's name will be created (in the \Projects folder) as will a new 'main.agc' source code template and project file. Then with the main.agc file open in the IDE, copy the source code over from the text editor into your project's code field, replacing the default code that's there. Then save and launch your project. All of the necessary project file settings will be applied by the IDE that way with your source code now bound to the project and you can keep your original source code in place for future reference.
