Show documents which are open in application in dock

From /r/linux [1]:

"Every opened document on a Mac (regardless of developer) has a little icon on the title bar that you can move exactly like you're manipulating the icon of the file in the file manager. So if I've got a PDF open (in Acrobat or a multitude of other options) and I want to attach it to an email I'm typing in, I just simply drag the icon on the title bar of the PDF into the email. I don't have to navigate to where in my file system that PDF is stored. That same icon can also tell me where in the file system that file is stored - I just simply hold down the Command key when clicking it and it shows a full file path name where I can instantly navigate to any folder in it's tree structure."

[1] https://www.reddit.com/r/linux/comments/5aqjyn/switching_from_macos_the_basics_to_elementary_os/d9jbntj/