Join the Files. The next step in the confirmation process is to join the Classified Invoices file and the Customer file (illustrated in Table 9.5 with sample data) to produce another new file called Accounts Receivable, which is presented in Table 9.6. Recall that when using ACL’s Join feature both files must be ordered on the same key. This requires first sorting the Classified Invoices file by Customer Number to place it in the same