Lock Project
At any point, while working on a project, it can be set to a read-only state by locking it. When locked, it prevents any additional edits from occurring within in the project. All data from Resources through to Margin adjustments cannot be modified. This function is typically used to prevent any accidental changes being made to the project.
You can lock a project from further editing from within the Project Properties window by clicking the Lock Project icon on the ribbon menu.
Project Properties – Lock Project icon
When a lock has been set on a project, the Lock icon in the ribbon menu will have a blue highlight surrounding the ribbon menu button. When locked, the Status bar will display a locked padlock 
, indicating that the project is in an uneditable state.
Project Properties – Lock Project icon indicating the project is locked
To make the project editable again, simply click the Lock Project icon from the Project Properties ribbon menu and ensure that the button is no longer highlighted.
The lock icon in the Status bar will also update to an unlocked padlock 
reflecting that the project is in an editable state.