diff --git a/README.md b/README.md
index 3760612..86c05c8 100644
--- a/README.md
+++ b/README.md
@@ -14,6 +14,9 @@ with proper fixed layout support.
 Supported input formats include JPG/PNG/GIF/JP2/WEBP image files in folders, archives, or PDFs.
 Supported output formats include MOBI/AZW3, EPUB, KEPUB, and CBZ.
 
+If your source are Kodansha PDFs from Humble Bundle/Fanatical, 
+you'll need to first [convert the PDFs to CBZ](https://github.com/ciromattia/kcc/issues/680) for use in KCC.
+
 Its main feature is various optional image processing steps to look good on eink screens, 
 which have different requirements than normal LCD screens.
 Combining that with downscaling to your specific device's screen resolution