The current Adobe Acrobat Pro only allows a quick menu selection of >Windows > Split. This will give the user the ability to view a single document in two windows HORIZONTALLY (i.e. above and below). Because most pages are oriented in a Portrait orientation, it is more efficient to view documents VERTICALLY (i.e. side by side). It would be very easy for Adobe to add the programming option to be able to split this window vertically and very quickly by adding another menu option under "Windows > Split" to select the ability to split vertically or horizontally. Everyone's work to review different pages of the same document would be exponentially faster and more efficient.