  We perform a combination of searches for standard model Higgs boson
production in $p\bar{p}$ collisions recorded by the D0 detector at the Fermilab
Tevatron Collider at a center of mass energy of $\sqrt{s}=1.96$ TeV. The
different production and decay channels have been analyzed separately, with
integrated luminosities of up to 9.7 fb$^{-1}$ and for Higgs boson masses
$90\leq M_H \leq 200$ GeV. We combine these final states to achieve optimal
sensitivity to the production of the Higgs boson. We also interpret the
combination in terms of models with a fourth generation of fermions, and models
with suppressed Higgs boson couplings to fermions. The result excludes a
standard model Higgs boson at 95% C.L. in the ranges $90 < M_H < 101$ GeV and
$157 <M_H< 178$ GeV, with an expected exclusion of $155 <M_H<175$ GeV. In the
range $120 < M_H < 145$ GeV, the data exhibit an excess over the expected
background of up to two standard deviations, consistent with the presence of a
standard model Higgs boson of mass 125 GeV.
