diff --git a/elm/pdf.py b/elm/pdf.py
index 4ed66b8..aeb2e2c 100644
--- a/elm/pdf.py
+++ b/elm/pdf.py
@@ -345,7 +345,7 @@ def convert_to_txt(self, txt_fp=None, separator='    ',
         ----------
         txt_fp: str, optional
             Optional Directory for output txt file.
-        separator : str
+        separator : str, optional
             Heuristic split string to look for spaces between columns
         clean_header_kwargs : dict, optional
             Optional kwargs to override clean_headers kwargs