How to make Automatically serial number ?

[Islam23024287n9e7]

I want when I click on the serial number field, it automatically switches to the next number, for example 00001 and the next number it is automatic 00002 and clear all data to enter new invoice data with the new invoice number.
And I want to make a button to save the invoice, and the saved PDF copy is not editable on it.
Is this possible?

[Test Screen Name]

You ask a lot, this is much more difficult than it seems. The key thing is this: SOMEWHERE you must keep the serial number, changed for next time. But you don't want to keep it in the PDF, because you want to lock it. But where else can you keep it? PDF files cannot write to files. You would need a web service to give serial numbers, a serious programming task.

[Dave Creamer of IDEAS]

This sounds more like a job for a database. Take a look at FileMaker Pro--it works cross-platform and there are server based options available. It can output a PDF per invoice.