You can download the trial version of the software via the page linked below and then use your current serial number to activate it. Look down at the bottom for the links for Acrobat 9.
Be sure to follow the steps outlined in the Note: Very Important Instructions section on the download pages at this site or else the download will not work properly.
Acrobat X Pro, Reader, and Suite: http://prodesigntools.com/adobe-acrobat-x-10-pro-reader-suite-direct-d ownload-links-ddl.html
