The ionization and photofragmentation of molecules in the core region has been widely investigated for monomers and dimers of organic molecules in the gas phase. In this study, we used synchrotron radiation to excite electrons of the oxygen K-edge in an effusive molecular beam of doubly deuterated formic acid. We used time-of-flight mass spectrometry and employed the spectroscopic techniques photoelectron-photoion coincidence and photoelectron photoion-photoion coincidence to obtain spectra of single and double coincidences at different pressures. Our results indicate the presence of ions and ion pairs that have charge-to-mass ratio higher than the monomer DCOOD, as the (DCOOD)·D(+), and pairs (DCO(+), DCO(+)) and (CO(+), DCO(+)). Comparing the spectra obtained for different pressures we can ascertain that these ions are formed by the fragmentation of DCOOD dimers.