For Invoice PDFs the location is the same for both frontend and admin as both areas use the same templates.
content/** theme **/html/pdf-invoice/personal/* (Personal/Retail template files)
content/** theme **/html/pdf-invoice/trade/* (Trade template files)
As packing slips are admin only, the location is different.
admin/templates/windows/pdf/personal/* (Personal/Retail template files)
admin/templates/windows/pdf/trade/* (Trade template files)
If you are unsure, leave the files as they are.