Lock Page
Using the 'Lock Page' command will lock the file in it's current state, preventing any further changes from being made to it. The tab-color will change to green, to give you an indication of it's lock-state. To remove this lock, go back to the 'File' menu again, and you will see that the 'Lock Page' command has changed to 'Unlock Page'. Click this to unlock the page. Note that locking a page does not affect it's current altered-state. If you have altered the CPT file, and then locked it, you will still be prompted to save the changes if you try to close the file, delete the file, or close the program.