Calling method on OPC UA server for file sending to a press

Ignition
3

Try using system.file.readFileAsBytes instead of opening the file in Jython, which just gives you a String value.

https://docs.inductiveautomation.com/display/DOC81/system.file.readFileAsBytes

You need to be on a least Ignition 8.1.1 for this to work I think.