How to get doc name?

[Denmark_Del_Puso]

ill create sales order and the doc name is “SO-00006” and i submit it. then ill make sales invoice. the problem is, on my print format on sales invoice i want to get sales order number “SO-00006” into my sales invoice but it doesnt work please help me. thanks! this is what happen see this picture below.

THIS IS MY SALES ORDER

THIS IS MY SALES INVOICE

[Sangram]

Sales Order reference is in Sales Invoice Item table.

Seems like it is your custom print format .So you can fetch it from table as below,

{{ doc.items[0].sales_order }}

[Denmark_Del_Puso]

thankyou thanks a lot very helpful @Sangram