I am not familiar enough with the Action to know how to retrieve it for the scenario that you are trying to use it in.
I have used this Action only once before, in the Gift Certificate setup. It works in that case, because the Print is done within the same Rule that creates the Document. The way it is done is with this:
[=Data.Get("DocumentId")]
So you could accomplish the same thing, but you would need to have the Print done at the same time as you submit the Petty Cash Transaction.
Using the action in a Cashout report would not work, simply because there could be several Documents that were created throughout the day, and the Action doesn’t know which ones to print.