diff --git a/API.md b/API.md
index deeb009..f767f9c 100644
--- a/API.md
+++ b/API.md
@@ -111,6 +111,8 @@ imgInfo | [SignImageInfo](#signimageinfo) | optional | Image's informations for
 textInfo | [SignTextInfo](#signtextinfo) | optional | Text's informations for drawing.
 
 :one: For example: A pdf contains 17 pages and specify `"-3,5-7,9,12,15-"` to `pageidx` means `[0,1,2,3,5,6,7,9,12,15,16]`.
+> [!IMPORTANT]  
+> For placing signature on multiple pages, all target pages must have the same dimensions and the same rotation angle.
 
 ## SignOption
 :taco::taco::taco: