A detailed experimental and theoretical study of the interaction of very-low-energy electrons with the polar target HF is presented. This interaction is investigated experimentally by measuring rate constants for ionization and state-changing in collisions between K(np) Rydberg atoms with 90\sbsp∼<n\sbsp∼<400 and HF. The data are found to be consistent with the results of rotational close-coupling calculations that include possible effects associated with dipole-supported real or virtual states. The value of this state is effectively the only free parameter in the theoretical model. Comparison with the data suggests that for low energy electron-HF scattering there is a virtual state which, for J=0, has an energy of 1-1.5 meV. The present work points to the importance of dipole supported states in electron-polar molecule scattering.