Usually the Document host is designed to hold Panes that are placed in the center. So can you let us know why you want to use a Pane without the Document host as there might be a way of providing what you need with the document host. I am attaching project showing how you can modify the Document host so it does not have the tabs on top.
So it depends on the configuration of the Dock you have, but usually if you wan to add Pane in the center you may work around it by adding a Split Container with InitialPosition docked left and change its size in order to fit the screen, add a PaneGroup to it and then add the desired Pane in the PaneGroup.
Unfortunately we can not be more specific as we are not familiar with the configuration of the dock you have and your exact specifications. So maybe it would help if you can send us a simple application of a dock and what you have tried in order to get the Pane in the center.
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