What are you trying to change ? Cropping ? Making it a different size ? Editing ( adding or removing ) text ? All these can be accomplished within Page Numbering Online Pro.
If Print on Both Sides is not available, either turn up the paper weight of your paper or look for your printer manual listing the number of pages per inch for pages printed on both sides of the paper plate. (Usually printed on the home page of your printer.) Click Print. Then, if the page height on both sides is a multiple of the page size of the paper plate, then press the “X” button and confirm you want to print on both sides.