Technically it should be possible to get the fields you want like: $.file.get() .data.. But:
a. That would implicitly produce a call to the backend.
b. It relies on the process file not to be changed (since we are hardcoding on reading from the first file element in this case). That can be forces on level of every activity but might not work well with your scenario.
c. It is always a better Idea just to load the information you need from the object at the start of a process an treat the processes variables as SPOT for the time of its existence, so you don’t risk getting confused who’s in the right, when deviations occur (process vs. dms object)
So I advise you to simply load the information into process variables beforehand and check against these, if your scenario permits it (the almost always do)