I suppose that you could if you write a canned response and put the file into the canned response.
Then select the canned response when you reply (UI only)

100asa I think someone asked this before on the board. From what I recall, not as straight away as just clicking and adding. You can create a Canned Response and inside of that have the link or the information of the KB to it and then from the drop down during a reply, select that Canned Response.

Thats at least how I did it and was able to attach a KB article to the ticket.