Open custom file type

Hello, I'm making an application where you can save your projects in a custom file type. For example like Photoshop uses ".psd" or the simple Text Editor uses ".txt". Now I wan't to make it possible to double click my custom save file to open the game and jump directly into a scene to load the data from the custom file. It is possible to edit in registry, so my custom file type is registered on windows, but how am I managing the fact to open it with my game and also knowing that this file got opened, to transfer that data in it? Thanks for any help!