Customise Invoice PDF

It would be nice to have the option to customize the standard invoice PDF. There are default fields that for a lot of people are either unused or irrelevant.

We have the ability to add in custom fields, yet Blank Order numbers cannot be removed?

When it comes to job/reference numbers, the ability to generate custom sequential numbers in a similar fashion to INV # would be great. It seems a little silly to have an 8 digit job number as a small business.