Dolibarr tricks: add line numbers to PDF invoice or sales order or proposal

If you are struggling with adding line numbers to dolibarr sales order or proposal or proforma invoice PDF, here are the magic:

Go to global configurations add the constant "PDF_ADD_POSITION", set value to 1.
Then try to generate pdf document and see the magic.

You can also set "MAIN_VIEW_LINE_NUMBER" to 1 to add line numbers on the detailed view of quote / sales order / proforma invoice.

The developer really likes to keep things secret!