I'm locked out of my own PDFs.

Had to switch computer hard drives this year due to a crash. We have the old files under our old user name (from backup) and new files under another user name. Adobe says, when I try to open a file under the old user name: "You don't have permission to open this file. Contact the file owner or an administrator to obtain permission." Well, I am the owner and I never set up a security wall. I just downloaded the update for Acrobat Reader DC so should be fine there. Any ideas? (To clarify, the files I'm trying to open are scans of pages from publications I edited. I'm trying to combine them into a single PDF. I don't need to edit them in any way. I just need to be able to open them.)