You can lock an invoice and prevent any changes from occurring to the invoice by using the "Lock Invoice" feature.  To lock an invoice, select INVOICE TOOLS >> LOCK INVOICE from the Menu Bar at the top of the screen.  When an invoice is locked, the Status Indicator "LOCKED" will appear on the upper right hand corner of the invoice.

The lock feature is helpful in situations where inexperienced individuals may be using the program, and you want to prevent any inadvertent changes to existing invoices.  When an invoice is locked, all of the processes which can alter an invoice are locked as well.  For instance, if someone tries to use the "Calculate Discount" feature (accessed from INVOICE TOOLS), a message appears notifying the user that the invoice is locked.

Before locking an invoice, make sure that all the calculations have been completed first.  You can assure yourself of complete calculations by clicking on the "Calculate" button.

If desired, you can lock all the invoices by selecting INVOICE TOOLS >> ALL INVOICES LOCK from the Menu Bar at the top of the screen.

To remove the locked status from the current invoice select INVOICE TOOLS >> UNLOCK INVOICE from the Menu Bar.  To unlock all of the invoices, select INVOICE TOOLS >> ALL INVOICES UNLOCK.

Note that if you are using AnyOrder on a network, invoices may also be locked from time to time.  This is a bit different than the normal invoice lock that you set.  A network lock is set internally by AnyOrder when two or more people on different computers are trying to access the same field on the same invoice.  To indicate a network lock, AnyOrder triggers the LOCKED indicator, but to distinguish it from a regular lock, the text is more colorful.  The lettering is in red and placed over a bright yellow background.  Whenever you see a network locked invoice (indicated by the bright lettering), you should leave that invoice and work on another.