1. Open the Control Panel.
  2. Under "Hardware and Sound", click "View devices and printers".
  3. Right-click on your printer and select "Print Server Properties".
  4. In the "Print Server Properties" window, click the "Custom Paper Sizes" tab.
  5. Click the "New" button.
  6. In the "New Custom Paper Size" window, enter a name for your custom paper size.
  7. Enter the width and height of your custom paper size in millimeters.
  8. Select the "Portrait" or "Landscape" orientation.
  9. Click the "OK" button.

Your custom paper size will now be available in the "Print Server Properties" window. You can select it when you are printing a document.