When you delete a file, that file is actually still on your computer. The only way you can truly and securely remove a file is by wiping it or using some type of secure deletion.
To learn more, check out this OUCH! newsletter: https://securingthehuman.sans.org/newsletters/ouch/issues/OUCH-201612_en.pdf
More cybersecurity education available here: https://www.youtube.com/playlist?list=PLQNZaWpmI1TfMOQMJ-ra1VSGgkuOPtFlA