Hi Eva,
If you want to upload a File, you must write a name for a browsed file and you must select browsed file. Then you must click to green \\\\\\\"plus\\\\\\\" icon on the left of file name.
To get attached file in the next task, I\\\\\\\'m no sure because I\\\\\\\'ve never do it, but something said me I need to call TMS directly with GetTask into bpm diagram and show me this link
http://localhost:8080/axis2/services/TaskManagementServices?wsdl (makesure server is up and running fine).But I did\\\\\\\'nt know how do it.
I hope this help you and somebody with more experience help you too.
Thanks,
Iván