The documents were published in April, but they were only discovered now by German blog WinFuture, which tipped its information to The Verge. The product is clearly listed: iPad Touch Cover (Model 1719).
Microsoft previously sold Touch Covers for its Surface tablets that doubled as pressure-sensitive keyboards and protective covers.
Those covers magnetically click into place and provide protection for the Surface's touchscreen. They have a standard keyboard layout, shortcut keys, and a two-button touchpad that supports gestures.
It's unknown if the iPad version would be similar. All that's known is that it presumably has a lithium-ion battery, suggesting it could connect over Bluetooth. It could also work with an iPad Pro's Smart Connector, but that seems less likely.
Of course, Microsoft could have scrapped plans to release an iPad keyboard between April and now, or perhaps even earlier. For now, the single document is all we have to go on. We'll provide an update if that changes.