  We study the viability of pseudo Nambu-Goldstone bosons (Majorons) arising in
see-saw models as dark matter candidates. Interestingly the stability of the
Majoron as dark matter is related to the scale that sets the see-saw and
leptogenesis mechanisms, while its annihilation and scattering cross section
off nuclei can be set through the Higgs portal. For $\mathcal{O}(GeV) -
\mathcal{O}(TeV)$ Majorons, we compute observables such as the abundance,
scattering cross section, Higgs invisible decay width, and emission lines and
compare with current data in order to outline the excluded versus still viable
parameter space regions. We conclude that the simplest Majoron dark matter
models coupling through the Higgs portal, except at the Higgs resonance, are
excluded by current direct detection data for Majorons lighter than $225$~GeV
and future runnings are expected to rule out decisively the 1GeV-1TeV window.
Lastly, we point out that light keV-scale Majorons whose relic density is set
by thermal freeze-in from sterile neutrinos can account for the keV line
observed by XMM-Newton observatory in the spectrum of 73 galaxy clusters,
within a see-saw model with a triplet Higgs.
