Windowing is a function of the operating system. In Mac Word opening a document when no others are open, the document will assume the size & position when it was last used. If other documents are open a new/reopened document will assume the size of the first & be offset from it
For comparison purposes, investigate the options in Window> Move & Resize in the menu bar. If you aren't familiar with it there is a Combine Documents feature available in the Tools menu as well as on the Review tab of the Ribbon.
As for navigation in long documents, scrolling often is problematic because each character has to be redrawn page after page. The process is severely hampered by complex document structure & graphic content. Other methods which are far more efficient are:
- Working in Draft or Outline View rather than Print Layout View
- Using the Navigation Pane or Thumbnails Pane in the Sidebar
- The Go To feature in the Edit> Find menu [Option+Command+G]