Securely delete files on Windows machine using Sysinternals - "SDelete"

Download the "SDelete" utility from Microsoft site - https://technet.microsoft.com/en-us/sysinternals/bb897443.aspx

After downloading extract the contents into a folder such as "C:\SDelete". SDelete implements the Department of Defense clearing and sanitizing standard DOD 5220.22-M.

SDelete is a command line utility that takes a number of options. In any given use, it allows you to delete one or more files and/or directories, or to cleanse the free space on a logical disk. SDelete accepts wild card characters as part of the directory or file specifier.
Usage: sdelete [-p passes] [-s] [-q] <file or directory> ...
sdelete [-p passes] [-z|-c] [drive letter] ...
-a Remove Read-Only attribute.
-c Clean free space.
-p passes Specifies number of overwrite passes (default is 1).
-q Don't print errors (Quiet).
-s or -r Recurse subdirectories.
-z Zero free space (good for virtual disk optimization).

To execute, you can run "SDelete" from the folder where the executable has been downloaded:-

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C:\SDelete>sdelete -p 10 -s -a "c:\test"
SDelete - Secure Delete v1.61
Copyright (C) 1999-2012 Mark Russinovich
Sysinternals - www.sysinternals.com

SDelete is set for 10 passes.

c:\test\test.docx...Scanning file: Reached the end of the file.

c:\test\test.pptx...deleted.
c:\test\test.rar...Scanning file: Reached the end of the file.

c:\test\sample\test-recursive.txt...Scanning file: Reached the end of the file.

Zeroing free space to securely delete compressed files: 10%

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As an alternative, you can use another freeware "FileShredder" - http://www.fileshredder.org/

In this utility, you can select different algorithms for deletion as below:-