One solution for client management along with their estimate and invoice  . You can generate invoice of your client and send directly to their email. It provide you  complete journey to your client from estimate to invoice on go . You can also archive invoice if not needed currently.
Archive Invoice
  - You can archive invoice's for future review.
Generate Invoice
  - You can generate invoice of client on go and add your signature on your invoice .
  - Maintain invoice whether they are paid or not.
  - Send Invoice directly to client email as PDF attachment .
Estimate
 - Create estimate and send to client directly as PDF attachment .
Clients
 - Manage your client list and send them estimate or invoice easily .
Report
 - Check your invoice  financial report according to invoice status.