Permissions for -combine-pages

cpdfcommand.ml

@@ -586,6 +586,13 @@ let rec decrypt_if_necessary (_, _, _, user_pw, owner_pw, was_dec_with_owner) op
     | Some x -> Printf.printf "decrypt_if_necessary: op = %s\n" (string_of_op x)
     end;
   if not (Pdfcrypt.is_encrypted pdf) then pdf else
+    match op with Some (CombinePages _) ->
+      (* This is a hack because we don't have support for recryption on combine
+       * pages. This is pervented by permissions above, but in the case that the
+       * owner password is blank (e.g christmas_tree_lights.pdf), we would end
+       * up here. *)
+      soft_error "Combine pages: both files must be unencrypted for this operation."
+    | _ -> 
       match Pdfcrypt.decrypt_pdf_owner owner_pw pdf with
       | Some pdf ->
           args.was_decrypted_with_owner <- true;