Are the docs necessary for you to retrieve before a separation? Do they contain trade secrets, IP, etc.? And is the equipment a valuable and necessary parts of the business?
The reason I ask, is that it might be worthwhile to put them at ease, not to mention the expense of retrieving them through courts, to just let your partner keep what is not trade secret/IP/required equipment.
As for just showing up, yeah I would knock on their door. They made a commitment to you when they chose to become partners and communication is one of those commitments that is vital to a company and a relationship. And they have checked out of that relationship. I would suggest having your paperwork in hand, be direct, but do not let your emotions take over. It is scary to approach someone with things like this. And stay calm, collected and don't forget to smile. The last thing you want to do is be perceived as an aggressor in any way by them.
/my two cents