We apply a method proposed by members of CTEQ Collaboration to estimate the uncertainty in associated $W$-Higgs boson production at Run II of the Tevatron due to our imprecise knowledge of parton distribution functions. We find that the PDF uncertainties for the signal and background rates are of the order 3%. The PDF uncertainties for the important statistical quantities (significance of the Higgs boson discovery, accuracy of the measurement of the (WH) cross section) are smaller (1.5%) due to the strong correlation of the signal and background.