Generate Order number when last person singed

This may be easy, but is often impossible. Most real world solutions need a client/server solution, with robust database management; it is a mistake to see an ordering system in terms of its user interface, that's just a very small part of the iceberg.

See these answers: 

• https://community.adobe.com/t5/acrobat-sdk/creating-a-unique-id-or-serial-number-for-a-form/td-p/11531536?page=1

• https://community.adobe.com/t5/acrobat/auto-generate-a-number-and-prevent-it-from-updating-when-the-form-is-opened/m-p/8726590?page=1