A method of preparing documents for the transmission of secure information comprises the steps of preparing a first laminar element (13; 37) with a peripheral region (15) separable from a central region (14), printing the secure information on the central region (14) of the first laminar element (13; 37), or on a central region (19) of a second laminar element (12; 36), positioning the two laminar elements (13; 37, 12; 36) in face-to-face relation, with the face of the element bearing the information facing the said other element, and securing the element together around the peripheral regions. Apparatus for preparing secure composite documents comprises a first storage container (25; 47) for the first laminar element (13; 37), a second container (24; 50) for the said second laminar element (12; 36), and means (27, 28, 48, 49) for bringing the first and second laminar elements together in face-to-face relationship after the secure information has been printed on one of them, with the face of the laminar element bearing the printed information facing the other laminar element; and means (51; 48, 49) for securing the two laminar elements together around their peripheral regions.