1. A method ( 300 ) for applying differential policies on at least one digital document ( 120 a - 120 n ) among a plurality of workflow participants ( 110 a - 110 n ), said at least one digital document comprising a plurality of atomic units ( 122 a - 122 n ), wherein the atomic units are assigned with at least one of a plurality of the differential policies, said method comprising: tessellating, using a processor, the at least one digital document ( 304 ) to identify the atomic units and the at least one of the differential policies assigned to the atomic units; aggregating the atomic units according to the at least one of the differential policies assigned to the atomic units ( 306 ); and associating respective sets of keys to the aggregated atomic units ( 308 ), wherein common sets of keys are associated with the aggregated atomic units assigned with the same policies.