In my countys news, like an hour ago, they told us that even common objects like a pen are good to defend against an attacker with a knife, can you belive that? Good luck, lol. Can't make that shit up.
If all you have is a pen, it is better than bare-handed.
A pen has about the same cross-section as a knife. If you can grip it tight enough not to slip, it will stab just as deeply. Lack of a real handle makes gripping difficult, and of course there is no ability to slash. But the defensive mindset will be prepared to make use of any available tool.
It might be better than nothing and somehow be useful in the hands of a trained person, but for the average joe, it's GTFO or be done.
Yes, I know that on that distance even a gun won't help, but a pen, that's just hilarious.