Polaron state in poly(p-phenylene vinylene) (PPV) is studied theoretically by means of the Pariser-Parr-Pople model for π electrons on a PPV chain. The model contains a long range electron-electron (e-e) interaction as well as an electron-lattice coupling. The electronic structures of polarons are calculated within the unrestricted Hartree-Fock approximation. Based on the calculated spin density of the polaron, we compute electron-nuclear double-resonance (ENDOR) spectra which explain satisfactorily the experimental spectra of undoped PPV measured in a dark state. When the e-e interaction is neglected, the reproduction of the observed spectra becomes poor, demonstrating the importance of the e-e interaction.