The Photoscape application isn't working the same as Photoshop and because of that you don't have the possibility to save a project like Photoshop does. This is just an image editor with various features. After you edit and item, there is no way to reverse the operations unless that file is still opened in the application. The Photoshop application is using layers and advanced features and because of that, you have the possibility to save to PSD format.
