Button to duplicate current forms (for an invoice)

[krneki]

I'd like to create a template for invoice, so one could simply select desired products and quantity with drop down menus. I've already created a table with forms, but the problem is that there may be multiple items in invoice and each should be in new line.



I was wondering what would be the best solution to insert new lines into table when needed? My idea is to create a button which would basically copy/paste forms into new line (they are identical anyway), but I'm not sure how to actually do that, so any help would be really appreciated.