Windows operating system does not delete a file permanently when a file is deleted using shift+del key combination or files from emptied recycle bin of Windows. The allocation area or the index of the file system (FAT or NTFS) marks the area used by the deleted file as empty.  

The actual raw contents of the files are always present even if the file has been deleted and waits overwriting by the operating system. Deleted file, which is not overwritten, can be recovered.