When you’re working on a long, complicated document, you can collapse everything except the part you want to focus on. The ability to collapse and expand content in your document is based on its outline level. You can quickly add an outline level and make part of your document collapsible by adding a heading using Word's built-in styles.
Collapse or expand parts of a document
If you want the document to open with the headings collapsed, follow these steps.
Place your cursor in the heading.
On the HOME tab, in the Paragraph group, click the dialog box launcher.
In the Paragraph dialog box, click the checkbox next to Collapsed by default.