Or to prevent it being changed or deleted accidentally setting an object, you can choose not to object. This function is called locked.
Select the object you want lock.
Main menu "Format" "Lock" command.
Select the object you wish to cancel.
To select a locked object, the normal mouse click can not be selected, then drag the mouse to select it.
If you drag the mouse, because the object does not move non-editable state.
Alternatively, the main menu "Edit" "Select All" command also allows you selected.
Main menu "Format" "Unlock" command.