When you delete files in OS X, by default the system will simply remove the file’s entry from the drive’s index, which simply allocates the space used by the file as free for other uses. However, while this logically deletes the file, on conventional hard drives the data structure of the file is still intact and with special data recovery software can be read through and potentially recovered. This means that if you store an important document on an external hard drive and then decide to delete the file, its contents will still be on the drive and may be recoverable. However, Apple does offer a few approaches for removing the residual data from a file that you are going to delete, or which has already been deleted. If your file is still available, then the first option is to secure-delete it using the Secure Empty Trash option in the Finder.