After you delete a file, Windows removes the index for the file and keeps the operating system from accessing the files. However, this is not deleted permanently, with many tools another users have direct access to the disk can still recover the file’s from the hard drive. Which is really risky, your confidential files might be leaked. But you could avoid the situation by permanently destroy the data from indexing by using SDelete.
SDelete is a command line utility that takes a number of options. It allows you to delete one or more files and directories, or to cleanse the free space on a logical disk. SDelete accepts wild card characters as part of the directory or file specifier.
First of all get the SDelete from above link and paste the sdelete.exe file on to C:\Users\Your_PC_User folder. In my case the user is xsf:
Now run windows command prompt and run the command sdelete.exe and a license agreement will prompt, just accept it:
Now run the command sdelete -z C: to free space on C drive: