I was wondering if it is possible to get data about currently open trades for a strategy from outside of Zorro, without looking at the generated HTML file?
From what I've understood this data is saved in the .trd files, but I haven't seen any specification for those files. Is there one available that can be shared with the community?

No, that format is binary and rather complex. But you can simply write all open trade data that you need to a .csv file and then read that file from an external program.