the date in $today contains / , / is path directories separator.
You are trying to save “18.pdf” in “16” folder, in “Payroll_Worksheet_46_01” folder, in “worksheets” folder (etc.)
Usually folders aren’t created automatically, so you have an error because the path “/www/payroll/htdocs/payroll/public/worksheets/Payroll_Worksheet_46_01/16” does not exists.