This paper suggests that PdD formation may be exothermic. Did I miss something?
Well, you are not missing anything, but I somewhat oversimplified. That is, I said "electrochemical cold fusion experiments." During electrochemical reactions, as the Pd-D is formed, there is a deuterium deficit, which reduces recombination, which reduces the overall heat evolved from the cell. If it is a closed cells, there is orphaned oxygen in the headspace. The overall reaction is endothermic.