Document locked after being moved to a new Network Attached Storage

I have a Master diary document moved from an old NAS to the new Synology NAS. I cannot find a way to open a copy so that I can add/edit the contents. I am not offered the copy option when I open the document, but if I try to edit it, I am told that it is locked - no option is offered. I cannot find a hidden locked file to delete. I did “Select all” and “Copy” and “Paste” into the laptop documents folder, but that still gives me a locked file. I also tried renaming the document, but that was still locked. Laptop is now on Windows11. I have ticked “show hidden files”. Though I still have the old Buffalo NAS, it won’t run on Windows11. I was able to move the contents by using Buffalo’s attached USB back-up disc which the laptop could read and copy files to the Synology NAS. How can I obtain an editable copy please?