In the action for creating the report we published a variable name in which we store the report.
(You need to switch on the developer level in the user settings to see that.)
The variable is then written on the screen. It is something like doo.workflow.runningData.xv0ag5h6w8
You can use this data for whatever you need to do with the file. E. g. you can create a new action, type java script and there you can create a new record with the report in the attachment: