By default, if you select an image or text and drag any of the handles it will scale the image or text within. You can override this behaviour by holding down ALT and dragging a handle, which will stretch the object rather than scale.
If you wish to stretch an object by default instead of scaling it, right-click on the aspect ratio lock icon, and uncheck the option "Smart Transform"
Now the behaviour reverses, so dragging a handle will cause it to stretch and holding Alt will cause it to scale.
The above applies from the patch 18.104.22.168605. If your update service is still active and you are on version 15, please go to Help > Check for updates to update. If you are on version 12, you will need to download version 15. Please find the link here for downloads.