At your wedding you both sign three marriage certificates.
The commemorative certificate (ie the pretty one) is for you to keep and the other two are used for registration of your marriage (which is my responsibility).
The commemorative certificate is only decorative and CANNOT be used for official purposes like change of name or applying for a passport.
For "official purposes" you need an "official marriage certificate".
To obtain your official marriage certificate you must apply to the Registry of Births, Deaths & Marriages in the State or Territory where your wedding took place and the Registry charges a fee.
As you will be far too busy enjoying your honeymoon and your new married life to be worried about paperwork, MY WEDDING GIFT TO YOU is that I will prepare the application and pay the registration fee.
For more information call me and I can explain further.