Apple PowerBook (Duo 270C) - Manual (Page 126)

Locking a file
You use the Get Info command to lock a document or a program.
Locking a program may affect its operation.
1. Click the icon of the file you want to lock.
2. Choose Get Info from the File menu.
3. In the Info window, click the Locked box in the
lower-left corner.
4. Close the Info window.
To unlock the file, click the Locked box again (so the X
disappears).
You can’t lock a folder, but you can lock items in a folder.
Locking an alias does not lock the original file. Locking an alias
merely protects it from being thrown away.
110 Chapter 7: Using Disks