FolderGuard is using a
shell-extension[
^] to "protect" the folders and files. There's some articles on CodeProject on that subject but it wouldn't be much of a protection - booting from a floppy and I'm in. Resizing partitions isn't something trivial and sounds a bit exotic to me.
It sounds as if you want to protect data from within the Windows Explorer. It would be quite easy to add an extra menu to the contextmenu, launching your .NET executable with the selected filename as a commandline-argument.
Next, you could store that file somewhere (in a zipfile hidden in the system with some strange file-extension, in a database like Sql Express, or on Azure) and delete the original file. If the user wants to look at the "secured" files, you show the list of the items that you stored in/on the zipfile|Sql Express|Azure.