CWShredder is a good app to shred the files there is also a applicaiton out there called Eraser which overwrites where the file is stored on the HDD enough times to make sure that there is no chance of recovery of that file.
I have personally used both and still use Eraser to this day. Both are good apps and will get the job done which ever way you want to do it.
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Phone: LG Optimus G Pro
Running: Stock JB from LG with Nova Launcher