You can apply a numbering scheme to the headings in your document by using multilevel-list templates and built-in heading styles in Word (Heading 1, Heading 2, and so on).
Important: Make sure you're using built-in heading styles in your document.
You can number headings so that a top-level headings (Heading 1) are numbered 1, 2, 3, for example, and second-level headings (Heading 2) are numbered 1.1, 1.2, 1.3.
Open your document that uses built-in heading styles, and choose the first Heading 1.
On the Home tab, in the Paragraph group, choose Multilevel List.
Under List Library, choose the numbering style you would like to use in your document.
Note: Depending on the type of documentation you've prepared, you might choose a template that includes the word "Heading" in the example.