Lock a document on Mac
To protect documents from being accidentally changed or deleted, you can lock them. When a document is locked, you receive a warning when you move it to the Trash. When you empty the Trash, the locked document is deleted.
On your Mac, do one of the following:
Lock a closed document: Select it, choose File > Get Info, then select Locked.
Lock an open document: Hold the pointer to the right of the document title, click the arrow, then select Locked.
To unlock a document, deselect Locked.
To protect folders and disks, change permissions for them.