The proposed technical solution allows processing of machine-readable forms of unfixed format. It comprises a method of specifying the logical structure of a document characterized by: preliminary specification of the list and descriptions of varieties of elements which may be present in the form, specifying an algorithm of setting the search constraints for every element, description of at least the following characteristics of search for every simple or compound element—the spatial characteristics of the search area and the parametric characteristics of the element, description of the method of identification of obtained elements, testing the type of the element, testing the properties which are typical of the type, testing the completeness of composition of the parts of the element.