A system and method for unique authentication of each replication of a plurality of soft-copy documents, forming a group. One soft-copy document, out of the group, becomes a carrier for an authentication code aimed at protecting the group. The authentication code is computed from the concatenation of the plurality of soft-copy documents and a key. A random number is also generated for each replication of the group of files. The random number is combined with the authentication code to mark the soft-copy document which has been selected to become the carrier. Thus, the invention introduces randomization in the insertion of the authentication code so that for each replication of an identical group of data files, unique authentication data can be associated, merged and hidden in the transmitted information.