Navigation: Tools → Search/Lock/Unlock PNR…
Main purpose is to exclude the PNRs transferred from a GDS with duplicated numbers (when the same number becomes reused for a new PNR later on).
To lock the found PNR: check the column Locked (to unlock – uncheck) and save the changes.
Use 'Lock PNRs Up To Date' (in the main menu Tools → Lock PNRs up to date…) for the same purpose, when it is needed to lock all PNRs transferred before the defined date.
Note
Order with a found PNR attached can be opened by a double click in the 'Search Results'.