Ever go to edit a previously created document (LibreOffice, MS Office, whatever) and have it open "read-only" and claim that you couldn't save any changes to it because someone else is working on it, even though this is not true? Here's why that happens:
Sometimes the programs we use crash or get shut down incorrectly while we are editing a file. When this happens, often the program doesn't have a chance to remove the small, hidden extra file that programs create (in the same location as the main file) when a file is being worked on - so that only one person at a time can work on the file.
With this hidden "lock" file still present, the program still thinks that someone else is working on the file, and will continue to think this until that file goes away, which we have to manually remove to ever get access to the original back. Here's how:
Click on the Start Menu and type "folder options" into the search box. (You can also find "Folder Options" in the control panel.)
In the "View" tab, select "Show hidden files..." in the Advanced settings area.
Click "Apply" but don't close the Folder Options window.
Browse to the location of the incorrectly locked file.
Find the "lock" file and delete it. (the name usually starts with a tilde (~) and/or the word "lock")
To make hidden files hidden again, go back to the Folder Options window, select "Don't show hidden files..." and click "Apply."
NOTE: There's no reason you can't leave "Show hidden files..." enabled all the time, it can just make some directories look a bit more cluttered than they need to be.