Wet the cardboard until it is pliable, then hit it with something hard until it opens

Mail it to yourself via USPS

[b] [/b]

Rip and tear until it is done

First you put that box inside of another box, and then you mail that box to yourself, and smash it with a mallet!

Fire

First off we need a Rocket that can reach orbit, next we need a secondary delivery system like say a MIRV or a rigged up Javelin missile within the payload of the Rocket, thirdly we shall utilize a cheap and stupid A.I. along with laser targeting and also a camera for close confirmation for said targeting. To open this [b]alleged box[/b] we start by a comedically Hollywood countdown sequence followed by blasting our Rocket into space, while this is happening be sure to eat some snacks and maybe watch some advertisements of Reese's or something, maybe twiddle your thumbs. After this and once our payload is in orbit it shall utilize a nearby spy satellite and hack it to find the [b]box[/b] you need opened. Immediately after this our Rocket opens up to reveal a smaller machine inside the Rocket. What is this machine? well its similar to a Javelin from Call of Duty. Next you hear this awkwardly loud and annoying beeping as this machine gets a laser-lock and fires the missile at your [b]box[/b]. As the missile reenters the atmosphere it adjusts trajectory and does some loops to slow down. Once low enough to ground level the missile utilizes its cheapo Walmarty A.I. to snap a photo at close range of the box and confirm that it is same [b]box[/b] from the space laser-lock targeting. At incredible speed and [i]precision you could only get from a droid[/i] the missile flies low over the [b]box[/b] and rapidly pulls up right as it skims the surface of the [b]box[/b], thusly using its bottom tail-fin to open said [b]box[/b]. P.S. If your neighbor asks where his cat went, just make something up, do not mention why there is a hole in your neighbors house or why there is a crater in his driveway. Simply tell your neighbor...[b]Aliens[/b]...and walk away looking frightened, he'll believe you.