PDFs not opening on my USB again - Recurring Error Message

So it looks like my nearly 1TB USB is being troublesome again when it comes to trying to open PDFs from it. About 2 months ago, I had a problem when it came to trying to open PDF files (maybe even other file types too when I downloaded an Excel file). I would get the messages:

"Adobe Reader could not open … because it is either not a supported file type or because the file has been damaged (for example, it was sent as an email attachment and wasn’t correctly decoded)."

or
"There was an error opening this document. The file is damaged and could not be repaired"

After retracing my footsteps according to the file dates before I started getting these PDF error messages and going through a lot of mental frustration and painfully wasted time, I finally realized that the problem was a bulky zip file and after unpacking it and then deleting the zip file, the PDFs started opening properly again. In other words, it looks like the cause was a bad sector and this was something neither I nor the people who helped me was initially aware of when I last asked for help on that here. It actually reminded me of an error message with another one of my previous USBs that keeps repeating the message “please insert the last disk of the multi-volume set” every time I put it in and then made most of my mov files inaccessible, which I think was because of me downloading a bulky zip file of my smartphone photos into my previous USB, if memory and retracing serves right.



Anyways, now it looks like almost any new PDF that I download and then try to open up becomes inaccessible again. There are a few I'm able to open after I download but for the most part, I get either one of the two above messages for newly downloaded PDFs into my current USB. I've fully scanned my current USB with my Norton multiple times, attempted to retrace my footsteps to the best of my memory, unpacked my older zip files, and used the AOMEI Partition Assistant app and the Command prompt chkdsk to try to find any bad sectors if possible. I can't seem to find what is causing it since I still keep getting those error messages on most of the new PDFs I download.
I think the only things I haven't tried are doing a format of my current USB (since I don't think I currently have anywhere with enough reliable storage space to move them to while performing the format) or deleting my older zip files after unpacking them, which confuses me since I've never experienced any kind of PDF error message when those particular zip files were still unpacked on my USB. Does anyone know what else I can do to resolve this issue properly in order to access any new PDF I download on to my current USB or does it really look like I'll have to buy a completely new USB? I just don't know why this keeps happening to my USBs after I try backing up things into a bulky zip folder and move that into my USB.