Reply To: Two documents side by side

The Window/View/Split option allows you to see two views of the same document. This can be helpful when you want to work close-up without losing sight of the entire page.
Instead,with two or more layouts open select Window/Arrange followed by the layout you desire. There are options for two-up side by side or stacked, and also some options for a larger view with a few smaller views for other files.
Each window/view created can contain multiple tabs (layouts) which could allow you to the file you are working on one side, and all reference files tabbed and available on the other side.