Sometimes user delete the file from computer and recycle bin. So, can your file retrieved? The answer is yes, when user delete the file or folder from computer then file still available in Computer Deallocated sapce.As all file avilable in deallocated area of computer so al the file can be recovered via forensic tools.So from few command line user can delete the file permanently from deallocated area:
Start Command Prompt(Start-Run-CMD)
Type cipher /w:Drive name Or folder name and then press enter
Use the Directory in place of folder which you want to clean.
eg : if u want to clean entire c drive then
command cipher /w:c:\