As far as I know, Adobe has not yet released any plug-in SDK for Acrobat Pro DC, and there was no developer preview of it before they announced the public release today. Developers of other Acrobat plug-ins, like Enfocus PitStop, were taken off-guard as well:
Just for the record PitStop 12 update 3 which was released last October is 64-bit and works with Acrobat DC.
regards
abc