Open the document editor by pressing the thumbnail grid icon in the action bar.
Make sure you are in the edit mode. To switch to the edit mode you have to press the edit button at the bottom.
The floating edit button will have changed to a plus sign.
Press the plus sign and configure the page in the visible dialog. Confirm the dialog.
Press the confirm button and choose a save option.
Note: Any changes that are not confirmed and changed will be lost when leaving the document editor!