You can quickly add page numbers to your document in Word Online, but you can’t add different numbers or number formats to different sections (or chapters) the way you can in the desktop version of Word.
For example, with the desktop version of Word, you can use Roman numerals (i, ii, iii, etc.) for the introductory section of a complex document, then switch to Arabic numerals (1, 2, 3, etc.) when the real content begins. Word Online preserves those section numbers once they’re in the document.
If you have the Word desktop application, click Open in Word to open the document.
Then follow the instructions in Add different page numbers or number formats to different sections. (For Word for Mac, see Add different page numbers or number formats to different sections in Word 2016 for Mac.)
When you’re done and you've saved the document, you’ll see the changes when you reopen it in Word Online.
For more info about page numbering in Word Online, see Add page numbers to headers or footers.
Tip: Word Online works seamlessly with Word and other Office desktop programs, and we update it based on input like yours. For the latest feature announcements, visit the Office Web Apps blog.