How to write a printer driver

I would like to know if there is a way be it using a printer driver or an existing application to create a bitmap image of the document I am working on.
I use Quickbooks accounting to create invoices but cannot save those invoices as bitmaps and the only way to do so is by copying the invoice using the print screen button one section at a time to Microsoft Paint.
I would like to possibly write a driver which would install into the programs print options like Winfax does but be able to save the document as a bitmap instead of print it out.

Thank you kindly for any assistance.

Enrico de Brito.