  RX J1713.7-3946 is the brightest shell-type Supernova remnant (SNR) of the
TeV gamma-ray sky. Earlier Fermi-LAT results on low-energy gamma-ray emission
suggested that, despite large uncertainties in the background determination,
the spectrum is inconsistent with a hadronic origin. We update the GeV-band
spectra using improved estimates for the diffuse galactic gamma-ray emission
and more than doubled data volume. We further investigate the viability of
hadronic emission models for RX J1713.7-3946. We produced a high-resolution map
of the diffuse Galactic gamma-ray background corrected for HI self-absorption
and used it in the analysis of more than 5~years worth of Fermi-LAT data. We
used hydrodynamic scaling relations and a kinetic transport equation to
calculate the acceleration and propagation of cosmic-rays in SNR. We then
determined spectra of hadronic gamma-ray emission from RX J1713.7-3946,
separately for the SNR interior and the cosmic-ray precursor region of the
forward shock, and computed flux variations that would allow to test the model
with observations. We find that RX J1713.7-3946 is now detected by Fermi-LAT
with very high statistical significance, and the source morphology is best
described by that seen in the TeV band. The measured spectrum of RX
J1713.7-3946 is hard with index gamma=1.53 +/- 0.07, and the integral flux
above 500 MeV is F = (5.5 +/- 1.1)e-9 photons/cm^2/s. We demonstrate that
scenarios based on hadronic emission from the cosmic-ray precursor region are
acceptable for RX J1713.7-3946, and we predict a secular flux increase at a few
hundred GeV at the level of around 15% over 10 years, which may be detectable
with the upcoming CTA observatory.
