I'm a fan of the Vic 91mm files. As above, they work well for plastics. That said, if you have one available, I think the smaller nail files would be a better choice for your purpose as they'll leave a smoother finish, in my experience.
Another option is fine sandpaper. I don't like chads annoying either and this is how I've dealt with them in the past. It'll also be kinder to cardboard.
In case you're not aware, there are two predominent 91mm files. Each has its place. Against the older, thinner, chromed case hardened file, the current stainless steel file is coarser and more aggressive, even on its fine side. Great for rapid removal of material. It's also more durable when used on hard metals. The older file is quickly dulled by very hard metals, but is finer and gentler on both sides and leaves a smoother finish on softer metals and materials.