Invoices and credit notes should be copied to History immediately on Day End, and be able to be be purged from Current only if they have been printed.

- Edit the Column grid for the Current Invoices and look for a field called 'Moved to History' and add it to the grid. This will tell you if Day End Processing has read and copied the invoice (or order or credit note) to History. If says Yes then the process has been done. Perhaps History was purged?

- You can print older and unprinted documents to PDF as you indicated. Or you could set the company profile to 'mark print to screen as printed'. Then select the invoice(s) and set the Print Destination to 'Screen' and click the Print button. (note that this is different than clicking the Preview button)