Ksar,
I got a better solution to this. Under Invoice Module setup there are substitution variables:
So what I did in free text was type in Prepared by: then the subs variable USER_FULLNAME This prints the user who prepares or rather generates the pdf invoice.
This was not there in versions 5.x it was introduced in v6.
At least problem solved. But I still need step by step help on extra fields insertion just by merely saying I need to look at this element still does not help me I need step by step on what to do, what to insert where.