(If i share this post wrong section then please moved it)

My PC was problem thats why i visit PC repair shop few days ago and after checked,shop staff said my harddisk have problem and they changed it,i have warranty they changed it for free.

It is Samsung 1TB harddisk.

But now i have problem.They said before changed it i have to moved my all files to my another external harddisk.
I already did it yesterday but i hear if i formatted my harddisk then also my all files can recover using software.

The company buy all PC/laptop product from China.Now i have problem and i fear very very much.

If china or PC repair shop any staff recover my all files and used it for bad?Then?
It never happened but if happened then?I don't want someone do this.

This is my request to you all,tell me if I do what then after removed my harddisk all files No Second people can't recover my any files?Is there anything you know?

I have many photo/personal files have in my harddisk.I don't want someone watch that and blackmailed/watch everything i have.

Anything can happened anytime right???

Tell me can it happened? If happened how can i delete all files from my harddisk PARMANENTLY?

There is few forum i share my problem but found no good reply.Thats why i came here and as my first post here,i hope you all helped me.

(If you know any software that can removed every files from my harddisk then please share here step by step.I don't have time and i am new about this,have limited time the pc disturbed. Please tell here if you think you can helped me,I can wait maximum 3 days.I used windows 7 ultimate)