Open TTX file to proofread

My client has sent me some ttx files to proofread. How do I open these ttx files in Studio 2017 without changing the file type? Studio can open open them via File>Translate Single Document, but I can then only save them as a new sdlxliff/sdlproj file. Can I not open and save the file as is?

The Studio interface is not very intuitive when it comes to doing this.....