  Exclusive proton-antiproton annihilation into two photons can be viewed as
the Compton process in the crossed channel. At large s (~10 GeV^2) and |t|,|u|
s this process can be described by a generalized partonic picture, analogous to
the 'soft mechanism' in wide-angle real Compton scattering. The two photons are
emitted in the annihilation of a single fast quark and antiquark ('handbag
graph'). The transition of the p-pbar system to a q-qbar pair through soft
interactions is described by double distributions, which can be related to the
timelike proton elastic form factors as well as, by crossing symmetry, to the
usual quark--antiquark distributions in the nucleon. We estimate that this
reaction should be observable with reasonable statistics at the proposed
1.5..15 GeV high-luminosity antiproton storage ring (HESR) at GSI.
