Split View is available in Documents for iPads only. Due to the smaller screen size, Documents doesn't support the Split View feature on iPhones.
If your iPad runs iPadOS 13 or later, you can open multiple windows of Documents and work on two or more PDFs simultaneously. This is a great way to compare documents or refer to one PDF while editing the other.
If you opened too many windows, just tap and hold on the Documents icon on your Home screen and tap Show all Windows to see all the opened instances of the app.
iPads with the older iOS versions have no option to open multiple instances of the same app. Instead, on your iPad with iOS 11 or later, you can use Split View to work with two different apps at the same time. For example, you can view two PDFs side by side by opening Documents and our PDF Expert app at once. Split View is also convenient for moving files between apps with drag & drop.
How to adjust Split View:
To make sure Split View works on your iPad, please open the System Settings of your iPad. Go to General > Multitasking & Dock and check if the Allow Multiple Apps toggle is on.
You can use Split View with iPad Pro, iPad (5th generation and later), iPad Air 2 and later, or iPad mini 4 and later.