Hi, and thanks for reaching out. My name is Bernard a Windows fan like you. I'll be happy to help you out today.
I understand the issue you have, there is nothing to worry I am here to help, the file seems to have permission wherein the owner can only be the one to edit or upload it, in addition, does it only happen with that specific Word file? in addition, can you try to open the file, click File > Save as >, save to your desktop, and try to upload again?
Or try to copy the files, paste them to a different location, and try again.
Let me know how it goes and I hope that helps.
Bernard