How can I edit a bilingual (IT-IT) doc?

Hello. I was hoping sb could help. I have a bilingual document (which I save in pdf but it was originally sent to me as .docx.txfl). I just need to edit it, but when I tried to open it in Trados just as a normal document as I usually do, I could then only see the ST. 

Could anybody pls help? 

Thank you in advance,

Rosaria