I looked into the idea if the old 32 bit version of the AcroPDF.dll file can be installed as well as the 64 bit version so they both co-exist.
I found that both versions of the dll have been built to use the same GUID which I believe means that they can't co-exist unless Adobe builds the 64 bit version with new GUID, this was my previous suggestion for Adobe when I was talking about separate packages.
Therefore I think your installer will possibly work in the short term but when a user runs update your install will be broken. Alternatively the users where you install the old AcroPDF.dll will break any other app that requires the 64 bit version.