“-“ is removed at helper ,

so use “_” instead

cps/web.py

@@ -1275,7 +1275,7 @@ def get_download_link(book_id, format):
             helper.update_download(book_id, int(current_user.id))
         file_name = book.title
         if len(book.authors) > 0:
-            file_name = book.authors[0].name + '-' + file_name
+            file_name = book.authors[0].name + '_' + file_name
         file_name = helper.get_valid_filename(file_name)
         response = make_response(
             send_from_directory(os.path.join(config.config_calibre_dir, book.path), data.name + "." + format))