Chrome says: "Resource interpreted as Document but transferred with MIME type application/vnd.openxmlformats-officedocument.wordprocessingml.document"
Don't worry about the Chrome warning.You are using a valid MIME Type for .docx files.
According to this issue in the Chrome bug tracker, a commenter on January 29, 2014 states that this may be caused by a missing Content-Length header. It doesn't fix the problem for me, however, where I return a dynamically generated PDF based on a form POST.
If nothing else, maybe add to or star the issue there. It may be innocuous.
The MIME type for your file is correct and actually does not matter here.
If your file is put inside an <a> element (whether it's static or dynamic), you need to add the download attribute to squeeze the warning.
Something similar happens to Edge as well, and adding download attribute solves it as well.
