As in an On Open event?

You need some VBA code to do this whenever the document opens.  But you can't use a template for that purpose because when you create a new document based on the template, the VBA code on that template does not carry over to the new document.  So you have to store the VBA code in the document itself, and a macro-enabled document to boot (.docm, not .docx).

You need to add an AutoOpen() procedure if you need VBA code to run automatically when the document opens.  Put this code in a .docm file's VBA editor, and the document will open maximized with page width view set:

Sub AutoOpen()
    ' Maximize window
    ActiveDocument.ActiveWindow.WindowState = wdWindowStateMaximize

    ' Set view to page width
    ActiveWindow.ActivePane.View.Zoom.PageFit = wdPageFitBestFit
End Sub

Thanks Kevin that explains why my template didn't work