diff --git a/web/src/components/document-preview/doc-preview.tsx b/web/src/components/document-preview/doc-preview.tsx
index 22af1da1c0..fea4a9d44d 100644
--- a/web/src/components/document-preview/doc-preview.tsx
+++ b/web/src/components/document-preview/doc-preview.tsx
@@ -1,59 +1,26 @@
 import message from '@/components/ui/message';
 import { Spin } from '@/components/ui/spin';
 import request from '@/utils/request';
-import { DocxEditorViewer, useDocxEditor } from '@extend-ai/react-docx';
+import {
+  DocxEditorViewer,
+  useDocxEditor,
+  useDocxPageLayout,
+} from '@extend-ai/react-docx';
 import classNames from 'classnames';
 import { ZoomIn, ZoomOut } from 'lucide-react';
 import { useCallback, useEffect, useRef, useState } from 'react';
 
+import {
+  isZipLikeBlob,
+  useDocumentResizeObserver,
+  useDocxPreviewZoom,
+} from './hooks';
+
 interface DocPreviewerProps {
   className?: string;
   url: string;
 }
 
-// ZIP file header bytes "PK"
-const ZIP_HEADER_0 = 0x50;
-const ZIP_HEADER_1 = 0x4b;
-
-const isZipLikeBlob = async (blob: Blob): Promise<boolean> => {
-  try {
-    const headerSlice = blob.slice(0, 4);
-    const buf = await headerSlice.arrayBuffer();
-    const bytes = new Uint8Array(buf);
-    return (
-      bytes.length >= 2 &&
-      bytes[0] === ZIP_HEADER_0 &&
-      bytes[1] === ZIP_HEADER_1
-    );
-  } catch (e) {
-    console.error('Failed to inspect blob header', e);
-    return false;
-  }
-};
-
-const ZOOM_STEPS = [25, 50, 75, 100, 125, 150, 175, 200] as const;
-
-const clampZoom = (scale: number, direction: 1 | -1): number => {
-  let idx = ZOOM_STEPS.indexOf(scale as (typeof ZOOM_STEPS)[number]);
-  if (idx < 0) {
-    if (direction > 0) {
-      idx = ZOOM_STEPS.findIndex((v) => v > scale);
-    } else {
-      for (let i = ZOOM_STEPS.length - 1; i >= 0; i--) {
-        if (ZOOM_STEPS[i] < scale) {
-          idx = i;
-          break;
-        }
-      }
-    }
-  }
-  idx = Math.max(
-    0,
-    Math.min(ZOOM_STEPS.length - 1, idx < 0 ? 0 : idx + direction),
-  );
-  return ZOOM_STEPS[idx] ?? scale;
-};
-
 // Word document preview component.
 // Uses @extend-ai/react-docx for canvas-based page-level rendering.
 // Falls back to an unsupported notice for legacy .doc (non-ZIP) payloads.
@@ -63,9 +30,19 @@ export const DocPreviewer: React.FC<DocPreviewerProps> = ({
 }) => {
   const editor = useDocxEditor({ initialFileName: 'document.docx' });
   const { importDocxFile, status, totalPages } = editor;
+  const { layout } = useDocxPageLayout(editor);
+  const { containerWidth, setContainerRef } = useDocumentResizeObserver();
   const [loading, setLoading] = useState(false);
   const [error, setError] = useState<string | null>(null);
-  const [zoomScale, setZoomScale] = useState(100);
+  const showContent = !loading && !error;
+  const { zoomScale, minZoom, maxZoom, handleZoomIn, handleZoomOut } =
+    useDocxPreviewZoom({
+      url,
+      totalPages,
+      pageWidthPx: layout?.pageWidthPx,
+      containerWidth,
+      enabled: showContent,
+    });
   const cancelledRef = useRef(false);
 
   // Fetch the document blob and load it into the editor
@@ -117,7 +94,6 @@ export const DocPreviewer: React.FC<DocPreviewerProps> = ({
       await importDocxFile(file);
 
       if (!cancelledRef.current) {
-        setZoomScale(100);
         setLoading(false);
       }
     } catch (err) {
@@ -144,15 +120,6 @@ export const DocPreviewer: React.FC<DocPreviewerProps> = ({
     }
   }, [status]);
 
-  const handleZoomIn = useCallback(() => {
-    setZoomScale((s) => clampZoom(s, 1));
-  }, []);
-
-  const handleZoomOut = useCallback(() => {
-    setZoomScale((s) => clampZoom(s, -1));
-  }, []);
-
-  const showContent = !loading && !error;
   const pageCount = showContent && totalPages > 0 ? totalPages : 0;
 
   return (
@@ -170,7 +137,7 @@ export const DocPreviewer: React.FC<DocPreviewerProps> = ({
         <div className="flex items-center gap-1">
           <button
             type="button"
-            disabled={loading || !!error || zoomScale <= ZOOM_STEPS[0]}
+            disabled={loading || !!error || zoomScale <= minZoom}
             className="p-1 rounded hover:bg-gray-100 disabled:opacity-30 transition-opacity"
             onClick={handleZoomOut}
             aria-label="Zoom out"
@@ -182,11 +149,7 @@ export const DocPreviewer: React.FC<DocPreviewerProps> = ({
           </span>
           <button
             type="button"
-            disabled={
-              loading ||
-              !!error ||
-              zoomScale >= ZOOM_STEPS[ZOOM_STEPS.length - 1]
-            }
+            disabled={loading || !!error || zoomScale >= maxZoom}
             className="p-1 rounded hover:bg-gray-100 disabled:opacity-30 transition-opacity"
             onClick={handleZoomIn}
             aria-label="Zoom in"
@@ -197,7 +160,10 @@ export const DocPreviewer: React.FC<DocPreviewerProps> = ({
       </div>
 
       {/* Viewer / Error area */}
-      <div className="relative flex-1 overflow-auto bg-background-paper">
+      <div
+        ref={setContainerRef}
+        className="relative flex-1 overflow-auto bg-background-paper"
+      >
         {loading && (
           <div className="absolute inset-0 flex items-center justify-center">
             <Spin />
@@ -221,7 +187,7 @@ export const DocPreviewer: React.FC<DocPreviewerProps> = ({
         )}
 
         {showContent && (
-          <div className="flex justify-center p-4">
+          <div className="flex p-4" style={{ justifyContent: 'safe center' }}>
             <div style={{ zoom: zoomScale / 100 }}>
               <DocxEditorViewer
                 editor={editor}
diff --git a/web/src/components/document-preview/hooks.ts b/web/src/components/document-preview/hooks.ts
index 1fd92ae385..b6bcf67761 100644
--- a/web/src/components/document-preview/hooks.ts
+++ b/web/src/components/document-preview/hooks.ts
@@ -8,6 +8,26 @@ import { useSize } from 'ahooks';
 import axios from 'axios';
 import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
 
+// ZIP file header bytes "PK"
+const ZIP_HEADER_0 = 0x50;
+const ZIP_HEADER_1 = 0x4b;
+
+export const isZipLikeBlob = async (blob: Blob): Promise<boolean> => {
+  try {
+    const headerSlice = blob.slice(0, 4);
+    const buf = await headerSlice.arrayBuffer();
+    const bytes = new Uint8Array(buf);
+    return (
+      bytes.length >= 2 &&
+      bytes[0] === ZIP_HEADER_0 &&
+      bytes[1] === ZIP_HEADER_1
+    );
+  } catch (e) {
+    console.error('Failed to inspect blob header', e);
+    return false;
+  }
+};
+
 export const useDocumentResizeObserver = () => {
   const [containerWidth, setContainerWidth] = useState<number>();
   const [containerRef, setContainerRef] = useState<HTMLElement | null>(null);
@@ -146,3 +166,117 @@ export const useCatchDocumentError = (url: string) => {
 
   return error;
 };
+
+const ZOOM_STEPS = [25, 50, 75, 100, 125, 150, 175, 200] as const;
+
+const clampZoom = (scale: number, direction: 1 | -1): number => {
+  let idx = ZOOM_STEPS.indexOf(scale as (typeof ZOOM_STEPS)[number]);
+  if (idx < 0) {
+    if (direction > 0) {
+      idx = ZOOM_STEPS.findIndex((v) => v > scale);
+    } else {
+      for (let i = ZOOM_STEPS.length - 1; i >= 0; i--) {
+        if (ZOOM_STEPS[i] < scale) {
+          idx = i;
+          break;
+        }
+      }
+    }
+  }
+  idx = Math.max(
+    0,
+    Math.min(ZOOM_STEPS.length - 1, idx < 0 ? 0 : idx + direction),
+  );
+  return ZOOM_STEPS[idx] ?? scale;
+};
+
+interface UseDocxPreviewZoomOptions {
+  url: string;
+  totalPages: number;
+  pageWidthPx?: number;
+  containerWidth?: number;
+  paddingPx?: number;
+  enabled?: boolean;
+}
+
+interface UseDocxPreviewZoomResult {
+  zoomScale: number;
+  minZoom: number;
+  maxZoom: number;
+  handleZoomIn: () => void;
+  handleZoomOut: () => void;
+  resetZoom: () => void;
+}
+
+export const useDocxPreviewZoom = ({
+  url,
+  totalPages,
+  pageWidthPx,
+  containerWidth,
+  paddingPx = 32,
+  enabled = true,
+}: UseDocxPreviewZoomOptions): UseDocxPreviewZoomResult => {
+  const [zoomScale, setZoomScale] = useState(100);
+  const [hasUserZoomed, setHasUserZoomed] = useState(false);
+  const [isInitialFitPending, setIsInitialFitPending] = useState(true);
+
+  const resetZoom = useCallback(() => {
+    setZoomScale(100);
+    setHasUserZoomed(false);
+    setIsInitialFitPending(true);
+  }, []);
+
+  useEffect(() => {
+    resetZoom();
+  }, [url, resetZoom]);
+
+  const handleZoomIn = useCallback(() => {
+    setHasUserZoomed(true);
+    setZoomScale((s) => clampZoom(s, 1));
+  }, []);
+
+  const handleZoomOut = useCallback(() => {
+    setHasUserZoomed(true);
+    setZoomScale((s) => clampZoom(s, -1));
+  }, []);
+
+  // Fit the page width to the container on first paint and on resize,
+  // unless the user has manually changed the zoom level.
+  useEffect(() => {
+    if (!enabled || totalPages <= 0 || !containerWidth || !pageWidthPx) {
+      return;
+    }
+
+    const availableWidth = Math.max(0, containerWidth - paddingPx);
+    if (availableWidth <= 0) {
+      return;
+    }
+
+    const fitScale = Math.floor((availableWidth / pageWidthPx) * 100);
+    const clampedFitScale = Math.min(100, fitScale);
+
+    if (isInitialFitPending) {
+      setZoomScale(clampedFitScale);
+      setIsInitialFitPending(false);
+    } else if (!hasUserZoomed) {
+      setZoomScale(clampedFitScale);
+    }
+  }, [
+    enabled,
+    totalPages,
+    containerWidth,
+    pageWidthPx,
+    paddingPx,
+    isInitialFitPending,
+    hasUserZoomed,
+  ]);
+
+  return {
+    zoomScale,
+    minZoom: ZOOM_STEPS[0],
+    maxZoom: ZOOM_STEPS[ZOOM_STEPS.length - 1],
+    handleZoomIn,
+    handleZoomOut,
+    resetZoom,
+  };
+};
diff --git a/web/src/pages/agent/form/title-chunker-form/hook.ts b/web/src/pages/agent/form/title-chunker-form/hook.ts
index d084a4b44d..53323c25c7 100644
--- a/web/src/pages/agent/form/title-chunker-form/hook.ts
+++ b/web/src/pages/agent/form/title-chunker-form/hook.ts
@@ -78,10 +78,10 @@ function transformApiResponseToForm(
     }
   }
 
-  if (method === TitleChunkerMethod.Group && !hierarchyGroup) {
+  if (!hierarchyGroup) {
     hierarchyGroup = '0';
   }
-  if (method === TitleChunkerMethod.Hierarchy && !hierarchyHierarchy) {
+  if (!hierarchyHierarchy) {
     hierarchyHierarchy = hierarchy || Hierarchy.H3;
   }