How to post a Vendor Invoice related with an Purchase Order using x++?

Hello,

I've created a Purch Order, but I want to post and invoice with partial lines of purch order.

I've been following these steps:

- Intanciate PurchFormLetter with PurchFormLetter::construct(DocumentStatus::Invoice)

- CreateParmTable, CreateParmLine, respectively.

- Executed PurchFormLetter.run()

I've read that is possible use PurchFormLetter.update(), what is the difference, in AX 2009, with run it's works, but in AX2012 is different.

I'll appreciate any help.

regards!