A business form assembly, and the method of forming the same, is described. The business form assembly includes superimposed front and back sheets with at least one of the sheets being provided on the surface thereof facing the other of the sheets with a dormant adhesive in the nature of a thermoplastic material which is rendered activatable by electromagnetic radiation. Sealing lines are formed between the sheets where the dormant adhesive is activated, the resulting sealing lines together defining a receiving compartment suitable for accepting a document for mailing or an object for storage. The sealing lines have generally negligible thicknesses and uniform widths along their lengths. Also described is the apparatus for making the business form assemblies. The mailing assemblies are suitable for manufacture either individually or as part of a continuous series or web of business form assemblies which can be processed through data processing or imprinting equipment prior to separation from each other.