In April 1997, documents involved in an extortion case were received by the document examiner. A suspect had already been identified by police from other evidence obtained. The document examination centered on whether documents received by the complainants could be associated with specimen material taken from the suspect and his place of work. A major part of the examination involved establishing whether there was any evidence to link the envelopes received by the complainants with specimen envelopes obtained from the suspect's work place. The questioned and specimen envelopes were initially examined to determine whether there were any gross differences in brand, size, printed details or paper type, which would eliminate the possibility of them being from a common source. No differences were found. Information gained from a visit to the factory that manufactures Candida brand envelopes led to the identification of several features that could be useful in comparing envelopes. These were matching the self-sealing gum patterns; paper fiber matching across the top and bottom edges of consecutively produced envelopes; matching the opaque patterns printed inside the envelopes; matching any other printed details on the envelopes; matching the cutter markings on the envelopes; matching the glue patterns on the edges that form the envelope; and matching specific features of custom-made envelopes. The two features that emerged as having the potential to provide the strongest links between envelopes were matching the self-sealing gum patterns and paper fiber matching. Through an examination of these features, it was possible to link the questioned envelopes as having come from the same batch, indicating they were manufactured at a similar time in a production run. 6 figures