In order to subscribe to the service the bank issuing your credit card and your billing address must be in the same country. If your credit card is issued by a United States bank this is the reason that you are being asked to create a new ID for the United States. If you need further clarification please feel free to contact the FormsCentral feedback alias.
Good day Matt,
When you created your Adobe ID with your email address, you chose Australia as your country. Unfortunately, the Adobe Store in a particular country (e.g. Australia) can only complete a purchase when the country of the Adobe ID matches the country of the Adobe Store.
The only way to circumvent this would be to sign into Adobe.com with your existing Adobe ID email address. Go to Welcome (in the upper right) > My Preferences > Adobe ID > Change. Change your email address to a new email address or to a dummy email address like email@example.com. This will free up your original email address. Now, create a new Adobe ID using your original email address and choose the US as your country. Again, you can then complete your purchase via the USA Country Store.
IMPORTANT NOTE: If you have other Adobe products or services registered currently with your original email address, they will now be associated with this new or dummy email address. However, if you don't have any other products or services registered, this shouldn’t be an issue.
Please let us know if you have any questions.
Acrobat Community Manager