A recovery reverts to a snapshot of your computer that day.
When you delete a file it goes to the recycle bin.
When you empty the recycle bin the pointers (reference link the the file) to that file are deleted. Eventually the file will get written over, but the file is still on your computer. EVERYTHING YOU DELETE IS!
Programs are made to erase the file and make them unrecoverable.
To erase the contents (of a file, folder, or the entire HDD):
You need a program that erases the hardrive.
You can search the internet for freeware.
http://www.pcworld.com/downloads/file/fid,22920-order,1-page,1-c,alldownloads/description.html
This is an example of a program that will erase the contents off your HDD
If you really need everything off the HDD you can swipe a magnet over it. But you probably don't need anything to that extent.