Adobe Acrobat Pro PC vs Adobe Acrobat 9

I purchased & downloaded Adobe Acrobat Pro DC but I think I need to Adobe Acrobat 9 to do (merge fields with Conga Composer) - how can I purchase and get a serial number for Adobe Acrobat 9 instead?  Since I already purchased Adobe Acrobat Pro DC it allows me to download Adobe Acrobat 9 but I don't have a serial number to use.  I don't even know if Adobe Acrobat 9 will work for me but I am hoping. is there a trial serial number key I can use to try it?

thank you!