393947 Electronic invoicing solution

hi, I have a php/mysql website for B2B. I get paid for services with Paypal STANDARD (not API/Pro) Gateway. This gateway accepts Credit card or Paypal payments. What I need now is an Electronic Invoicing Solution, implementing the following guidelines: 1. Invoices need to be sent via email automatically after paypal payment is completed. 2. Invoices will be sent as PDF attachement. 3. Each Invoice will have a unique number and will use the transaction data from the site (template attached). 4. Emails sent with the invoices must be DIGITALLY SIGNED, by a recognized authority. Please bid only if you have done this type of work before and if you can complete this in 3 days. No bids over 70$. thanks.