Parts/Services Pull Down List & PDF filename

[Thene <..hidden..>]

Greetings Everyone :)

I apologise if this has already been covered but I have been able to 
find information the following:

1. Is it possible to turn the Number field into a pull down list of 
Parts and Services when generating a Sales Invoice?

2. When printing to PDF a 10 digit number is prefixed to the filename. 
e.g. 1234567891_invoice_00000000.pdf
     
How is the prefixed number generated and is there way to change this? 
Say if the company was Glen's Cartage then the PDF file name could be 
glencart_invoice_00000000.pdf


Many Thanks,
Thene