To add page numbers to your PDF document using pdfFiller, simply follow these steps: 1. Open your PDF document in pdfFiller. 2. Click on the 'Page Numbers' tool in the main toolbar. 3. Choose the desired position and style for your page numbers. 4. Customize the appearance of your page numbers by selecting font, size, and color. 5. Click 'Apply' to add the page numbers to your PDF document. With pdfFiller's intuitive interface, adding page numbers to your PDFs has never been easier!