The files in your download folder are the copies made of the attachments after you click on them in Asana. This is the case whenever you click on a file on the web – it downloads to your computer first before it opens. This is not the file you attached, though – it’s a copy of it.
When you first created the file, before you attached it in Asana, you saved it somewhere on your computer. That’s the version you need to find and check to see if it has the modifications you described. If it doesn’t, then Asana had nothing to do with it.
If you’re expecting to update attachments, it might be better for you to use a cloud platform like Google Docs. We don’t use Word documents anymore – we create a Google Doc and attach it in Asana. That way there’s only ever one link and it’s always to the current version of the document. Google Docs have an equivalent to “Track Changes” in Word (it’s called “Suggesting” mode), and you can download a Google Doc in Word format for people who need that.
You can contact Asana Support at https://asana.com/support . From my experience if you’re logged in with a premium account you should get a reply same day or next day depending on the time. If you’re using a free account, it may take a few days.