You can apply a numbering scheme to the headings in your document by using multilevel list templates and the built-in heading styles in Word (Heading 1, Heading 2, and so on).
For example, you can number headings so that top-level headings (Heading 1) are numbered 1, 2, 3, second-level headings (Heading 2) are numbered 1.1, 1.2, 1.3, and so on.
Important: Before you start, be sure that your headings use the built-in heading styles.
Click in the first Heading 1 heading in your document.
On the Home tab, in the Paragraph group, click Multilevel List.
Under List Library, click one of the styles that includes the word Heading or Chapter in gray text.
For example, click 1 Heading 1, 1.1 Heading 2, 1.1.1 Heading 3.