This is possibly the silliest thread I've ever read. Given that the name of the method is RenameFile why would you think that it would do anything other than rename the file? The file name extension has no effect whatsoever on the contents of a file. You can give any file any extension you like. The only thing that does is prevent you opening the file by double-clicking it in Windows Explorer. You can still use File->Open in the same app and the file will open in all its glory. Try it with your allegedly encrypted text file and you'll see that you can still open it in Notepad and see all the text it contains. Don't you suppose that a method that encrypted a file would have "encrypt" somewhere in the name?