Just wondering, has the file been exported as a .doc already? In this case just open in MS Word.
Wordfast files are .txml, if it ends in .doc then it's a word file.
I'm guessing you might be trying to open the exported bilingual file with Wordfast, which is leading it to treat it as a whole new translatable source file (with both source and translated source in the left column).
You were right. It was the exported bilingual file. Fortunately, the PM had also sent me the original source text and the remote TM. So, I did the next:
I opened the source file in Wordfast and then I copied the proofread target text in the Target column. It took me more time than I thought, but at least I finished the proofreading and got the TXML file.
All the best,
[Edited at 2016-07-15 22:14 GMT]