Invoicing System

Invoicing System I need a system where I create an invoice on my end for a customer (through excel or another option?). I will only know their email address. After I create the invoice, I have a submit button where it is then uploaded to my website and a link sent securely to them. They open the link to the page where they see their invoice and fill in their personal info and payment fields. I need to be able to make certain fields “required fields??. After filling the fields, they hit submit and it e-mails a copy to me and on to them in an uneditable format. (pdf or just a printable web page?) This is probably a fairly easy thing for an experienced coder. I will have SSL option on my web server soon. Please let me know if you have any questions.