If you want to add another filter to filter out the Sales Orders in the Print Packing Slips page, you can:
1. Go to the Print Packing Slips page, Transactions > Management > Print Cheques and Forms and then click on Packing Slip. Then click on the Customize button
2. You'll then be redirected to the Customize Sublist page
3. Under the Additional Filters tab, mark the field that you want to add as a filter
4. Hit Save