As I might have previously mentioned1) 2), pressing “delete” in Windows (or on Linux or Macs) does not remove the file from the hard drive. The only thing that happens is that in the big list of files, the entry for that file is removed, so that the operating system knows that if it wants to, it can go ahead and write to the place on the hard drive where that file used to be stored. Now, you can wipe the entire hard drive if needed, but is there any way of securely removing individual files?
Short answer: No.
For the long answer, read on below.