diff --git a/index.d.ts b/index.d.ts
index 429b081..06f8455 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -151,8 +151,11 @@ interface FsPackage {
      * read a file relative to config dir and return its content
      *
      * @param path relative file path
+     * @param options optional options
      */
-    readFile(path: string): string
+    readFile(path: string, options?: {
+        bytes: boolean // if true return []byte instead of string
+    }): string
 
     /**
      * stat file or directory
@@ -430,6 +433,8 @@ interface PdfPackage {
      *
      * @param html html string
      * @param options options
+     * 
+     * @returns []byte of pdf data
      */
     fromHTML(
         html: string,
@@ -471,6 +476,24 @@ interface PdfPackage {
             headerHtml?: string // URL to header html
         }
     ): any
+
+    /**
+     * process existing pdf data
+     * 
+     * @param command pdfcpu command
+     * @param pdfData []byte of pdf data
+     * @param options options
+     * 
+     * @returns []byte of new pdf data
+     */
+    cpu(
+        command: "watermark",
+        pdfData: any,
+        options: {
+            mode: "image"
+            bytes: any // []byte of watermark image
+        }
+    ): any
 }
 
 export interface HookContext