UIDocumentBrowserViewController and UISplitViewController

Technically, it's doable. Replace the view that would show your document with a "container view" from the IB objects palette. Then create a new split controller scene in your storyboard, and connect from the container view to the split view controller using an "embed" segue.

Whether it's frowned-upon UI is hard to say. I've done this using a tab view controller as the root view controller, where it seemed perfectly natural to have a split view for the rest of the screen. Your idea isn't obviously bad, but make sure you test usability to see whether screen real estate becomes a problem or there are other usability issues in practice. If so, a navigation controller might be a better choice.

Note the the one condition where SVC can be used and not be root is when it is part of a Tabbar VC. See this link for 'order of containment':

https://developer.apple.com/library/prerelease/ios/documentation/WindowsViews/Conceptual/ViewControllerCatalog/Chapters/CombiningViewControllers.html

As for SVC, Justin from Apple here on the forumsaid this about that "As of iOS 8, embedding a Split View Controller in a tab bar controller (or your own container view controller) is supported and expected to 'just work'. Pushing a split view controller onto a navigation stack remains unsupported."

As for UIDocumentBrowserViewController, Apple confirms what you stated and says this about that...

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Important

Always assign the document browser as your app's root view controller. Don't place the document browser in a navigation controller, tab bar, or split view, and don't present the document browser modally.

If you want to present a document browser from another location in your view hierarchy, use a

UIDocumentPickerViewController

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So, which do you prefer as root, and optioonally, how do you feel about a UIDP VC?

Split view controller can perfectly well be a fullscreen presented view controller which is all that matters. The document browser view controller is the root view controller; your document is shown in a presented view controller.