Hello. 

I have an additional requiment on that. I do have the list of serial # on invoices, but when I have a lot of products I get an extremelly long table listing all the numbers. I would prefer to have it as a comma separated list (for example) and also under each product line. Could someone guide me on this?

I've located where that's done in the report itself and I would need to modify the code, but I don't know how. 

Help would be greatly appreciated. 

Hi,You can show the Lot / Serial number in the Invoice PDF by enabling an option from Inventory module.Inventory -> Configuration -> Settings

Valuation -> Enable Display Lots & Serial Numbers on Invoices option

Hope it helps