File Transfers After Resolved System Hijack

Hello,
The other day my computer started blocking pretty much all of my programs from opening and tons of “this program is blocked by name.worm” kept popping up. When I called Dell tech support they said my system had been “hijacked” via a trojan, and I had to create a new user account and buy the System Mechanic software. I was told not to use the other account again and that I could delete it. I meant to ask this to the tech support operator but he disconnected before I could…

While I had almost everything backed up on an USB, there are a decent amount of (albeit not too important) things I do not have. When I go to delete the old account, it gives me the option to transfer over all of the old files. Would this be safe? I also thought I could log into the old account, copy over the few photos and documents I need to my external drive and then delete the old account. The tech operator did copy over everything that was backed up locally (which was nothing) so I thought perhaps the individual files wouldn’t be infected, just the browsers?

I guess I’m asking (perhaps stupidly) 1) if trojans could infect documents, pictures and videos and 2) if I would do any harm to my computer and this new system by bringing over the old files, or logging into the infected one again to retrieve them specifically. Many thanks for any help you can provide.