As you edit and save the files, they're automagically written to the encrypted disk image, and then all you have to do at the end of the day is eject the disk image. The encrypted 'disk' appears just like another disk on your Desktop, with your files in it. If you used a secure disk image, you wouldn't have this problem. Your text editor doesn't know anything about the existence of the encrypted version of the file, so unless your encryption app does something clever to monitor changes to the file and then re-encrypt it automatically, you'll have to remember to encrypt the new version of the file once you're done editing it. However, the problem with this approach is the question of what happens when you make changes to the file and save it. There may be other apps out there that do this. Crypt will give you the 'double-click-to-decrypt' behaviour you're looking for, but it doesn't automatically launch the document after it's done decrypting. There are third-party apps that do drag-and-drop encryption of individual files, e.g. Here's an article from Apple describing how to create encrypted disk images. This is more like encrypting an entire folder, rather than an individual file, so it's not exactly what you're asking for, but it might work for you. Assuming that you want to encrypt the files, the only thing that Mac OS X has built-in is 'encrypted disk images'.

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