When you delete a file from your computer, it moves to the Windows Recycle Bin. You empty the Recycle Bin and so many might think that the file is permanently erased from the hard drive.
but its worng! When you delete files or folders, the data is not initially removed from the hard disk. Instead, the space on the disk that was occupied by the deleted data is "deallocated." After it is deallocated, the space is available for use when new data is written to the disk. Until the space is overwritten, it is possible to recover the deleted data by using a data-recovery software.
To permanently erase files and prevent your confidential files from getting into wrong hands, Microsoft offers a free command line utility - SDelete (Secure Delete) - that overwrites all the free space to prevent data recovery.
You can use SDelete both to securely delete existing files , as well as to securely erase any file data that exists in the unallocated portions of a disk (including files that you have already deleted or encrypted)
Download SDelete