  We perform the analysis of existing light-targets deep-inelastic-scattering
(DIS) data in the leading-order (LO), next-to-leading-order (NLO), and
next-to-next-to-leading-order (NNLO) QCD approximations and extract PDFs
simultaneously with the value of the strong coupling constant $\alpha_s$ and
the high-twist contribution to the structure functions. The main theoretical
uncertainties and experimental uncertainties due to all sources of experimental
errors in data are estimated, the latter generally dominate for the obtained
PDFs. The uncertainty in Higgs boson production cross section due to errors in
PDFs is $\sim 2$% for the LHC and varies from 2% to 10% for the Fermilab
collider under variation of the Higgs boson mass from $100 {\rm GeV}$ to $300
{\rm GeV}$. For the $W$-boson production cross section the uncertainty is $\sim
2$% for the both colliders. The value of $\alpha^{\rm NNLO}_{\rm s}(M_{\rm
Z})=0.1143\pm 0.0014({\rm exp.})$ is obtained, while the high-twist terms do
not vanish up to the NNLO as required by comparison to data.
