Cannot edit a document in InCopy

Bob is spot on here. You're probably getting a message when you open the file telling you "Because this document contains no stories, you will not be able to make any edits". I'm paraphrasing here as I don't have InCopy open but you'll know it when you see it. So your design will need to open the document in InDesign and export the stories that you want to edit. Once you do that, you'll have the ability to check out and edit the stories.