To lock or unlock a file using the Dropbox desktop app:
Note: Only files in shared folders can be locked. Or, you can make a copy of the locked file-however, any changes made to the copy will not be reflected in the original file once it’s unlocked. If you need to edit a locked file, you can request that the file be unlocked by clicking Ask to Unlock in the window that appears when you attempt to open the file.
Only the person who locked the file can edit and unlock the file. Once a file is locked, anyone with access to the file can still view, comment on, and share a link to the file. This allows teams and collaborators to coordinate who is editing a file and avoid conflicted copies. File locking is a feature available to Dropbox Business and Professional users that prevents a file from being edited.
