A family of Microsoft word processing software products for creating web, email, and print documents.
Assuming you are using the desktop version of Word for Windows, apply the built-in Heading 1 style to each book or major part and Heading 2 to each chapter. Then open View > Navigation Pane, or press Ctrl+F, and select Headings. You can click any heading to jump directly to that section, use the Pages tab to browse page thumbnails, or press Ctrl+G to go directly to a specific page number. Word can also collapse the text below headings, making individual chapters easier to manage.
For a 2,586-page manuscript that is already freezing, I would recommend dividing it into separate files based on books, parts, or chapters rather than fixed groups of 200 pages. Page boundaries will move as you edit, so logical divisions are more reliable. Word does not provide a regular ribbon command that automatically saves every 200 pages as a separate document; automating that would normally require a macro.