diff --git a/README.md b/README.md
index 4359868..5dad42f 100644
--- a/README.md
+++ b/README.md
@@ -21,10 +21,18 @@ pdflayers <input file> <output file> --show <layer names>
 or
 
 ```
-python -m pdflayers <input file> <output file> --show <layer names>
+python3 -m pdflayers <input file> <output file> --show <layer names>
 ```
 
 Acknowledgements
 ----------------
 
 [pikepdf](https://github.com/pikepdf/pikepdf) is doing most of the work.
+
+
+References
+----------
+
+[PDF 1.7 Reference](https://www.adobe.com/content/dam/acom/en/devnet/pdf/PDF32000_2008.pdf)
+[Acrobat JavaScript API Reference](https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/js_api_reference.pdf)
+[Acrobat DC SDK Documentation](https://help.adobe.com/en_US/acrobat/acrobat_dc_sdk/2015/HTMLHelp/#t=Acro12_MasterBook%2FJS_Dev_Overview%2FIntroduction8.htm)