When I open multiple documents in Arobat Reader DC, each document appears in its own tab. But if I open as much documents, as they don't fit in the bar, there appear two arrow buttons (left and right) for to move the bar and show wether the first, or the last document.

But clicking on the arrows to be able to click on a tab of the document you want to show can be boring and become uncomfortable. It would be nice to on mouse over the tab bar, activate a scroll function, so you would be able to use the scroll wheel of your mouse, instead of using the arrow buttons.