Get the application path

Question

Hey there, I've made a windows application form and then I set a certain file format, for instance, FILE_NAME.abc (the file format is .abc)

to be opened by this application form, by simply double clicking the file with the custom format and selecting the windows application form as the default program.

Now, I need to know the path of the file with the custom format that opened the application form.

Does someone know how to do that?

Thanks from advance.