def signed?
            begin
                self.Catalog.AcroForm.is_a?(Dictionary) and
                self.Catalog.AcroForm.SigFlags.is_a?(Integer) and
                (self.Catalog.AcroForm.SigFlags & InteractiveForm::SigFlags::SIGNATURES_EXIST != 0)
            rescue InvalidReferenceError
                false
            end
        end
def signed?
            begin
                self.Catalog.AcroForm.is_a?(Dictionary) and
                self.Catalog.AcroForm.SigFlags.is_a?(Integer) and
                (self.Catalog.AcroForm.SigFlags & InteractiveForm::SigFlags::SIGNATURES_EXIST != 0)
            rescue InvalidReferenceError
                false
            end
        end
Returns whether the document contains a digital signature.