diff --git a/__tests__/components/features/files-tab/file-content-viewer.test.tsx b/__tests__/components/features/files-tab/file-content-viewer.test.tsx
new file mode 100644
index 000000000..734dbb2dc
--- /dev/null
+++ b/__tests__/components/features/files-tab/file-content-viewer.test.tsx
@@ -0,0 +1,124 @@
+import React from "react";
+import { render, screen } from "@testing-library/react";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+import { FileContentViewer } from "#/components/features/files-tab/file-content-viewer";
+import type { ViewMode } from "#/components/features/files-tab/view-mode";
+import { useWorkspaceMutationCounter } from "#/stores/use-workspace-mutation-counter";
+
+// Mock the *services* the file-content hook depends on — not the hook itself —
+// so the real classification (text decoded, then flipped to binary on a NUL
+// sniff) runs end to end through the viewer.
+const useWorkspaceSessionMock = vi.fn();
+vi.mock("#/hooks/query/use-workspace-session", async (importOriginal) => {
+  const real =
+    await importOriginal<
+      typeof import("#/hooks/query/use-workspace-session")
+    >();
+  return {
+    ...real, // keep the real joinWorkspaceUrl the hook builds its fetch URL with
+    useWorkspaceSession: () => useWorkspaceSessionMock(),
+  };
+});
+
+const useActiveConversationMock = vi.fn();
+vi.mock("#/hooks/query/use-active-conversation", () => ({
+  useActiveConversation: () => useActiveConversationMock(),
+}));
+
+const useRuntimeIsReadyMock = vi.fn();
+vi.mock("#/hooks/use-runtime-is-ready", () => ({
+  useRuntimeIsReady: () => useRuntimeIsReadyMock(),
+}));
+
+const getActiveBackendMock = vi.fn();
+vi.mock("#/api/backend-registry/active-store", () => ({
+  getActiveBackend: () => getActiveBackendMock(),
+}));
+
+// The hook statically imports the cloud runtime service; stub the module so
+// this local-path test never loads the real cloud/proxy machinery. The test
+// uses the fetch (local) path, so downloadFile is never called or asserted.
+vi.mock("#/api/runtime-service/agent-server-runtime-service", () => ({
+  default: { downloadFile: vi.fn() },
+}));
+
+const fetchMock = vi.fn();
+
+const BASE_URL =
+  "https://agent.example.com/api/conversations/conv-1/workspace/";
+
+function renderViewer(path: string, viewMode: ViewMode = "rich") {
+  const client = new QueryClient({
+    defaultOptions: { queries: { retry: false } },
+  });
+  return render(
+    <QueryClientProvider client={client}>
+      <FileContentViewer path={path} viewMode={viewMode} />
+    </QueryClientProvider>,
+  );
+}
+
+describe("FileContentViewer", () => {
+  beforeEach(() => {
+    vi.stubGlobal("fetch", fetchMock);
+    fetchMock.mockReset();
+    useWorkspaceSessionMock.mockReset();
+    useActiveConversationMock.mockReset();
+    useRuntimeIsReadyMock.mockReset();
+    getActiveBackendMock.mockReset();
+
+    useRuntimeIsReadyMock.mockReturnValue(true);
+    useActiveConversationMock.mockReturnValue({
+      data: {
+        id: "conv-1",
+        conversation_url: "https://agent.example.com/api/conversations/conv-1",
+        session_api_key: "session-key",
+      },
+    });
+    useWorkspaceSessionMock.mockReturnValue({
+      data: { baseUrl: BASE_URL },
+      isLoading: false,
+      isError: false,
+      error: null,
+    });
+    getActiveBackendMock.mockReturnValue({
+      backend: { id: "local-1", kind: "local", host: "http://localhost:8000" },
+      orgId: null,
+    });
+    useWorkspaceMutationCounter.setState({ count: 0 });
+  });
+
+  afterEach(() => {
+    vi.unstubAllGlobals();
+  });
+
+  // The acceptance criteria require the clear message in BOTH view modes. The
+  // plain-mode fallback and the rich-mode binary branch both route through
+  // UnpreviewableFallback, so one parametrized spec covers both code paths.
+  it.each(["rich", "plain"] as const)(
+    "shows a clear unsupported-document message for an Office file (.pptx) in %s mode",
+    async (viewMode) => {
+      // Arrange: the workspace fileserver returns real .pptx bytes — a ZIP whose
+      // header carries a NUL, so the hook classifies the file as binary.
+      fetchMock.mockResolvedValue({
+        ok: true,
+        status: 200,
+        arrayBuffer: () =>
+          Promise.resolve(
+            new Uint8Array([0x50, 0x4b, 0x03, 0x04, 0x00]).buffer,
+          ),
+      });
+
+      // Act
+      renderViewer("demo.pptx", viewMode);
+
+      // Assert: the format-aware "no preview" message replaces the generic
+      // binary fallback in both modes, so the pane is never blank.
+      expect(
+        await screen.findByTestId("file-content-viewer-unsupported-document"),
+      ).toBeInTheDocument();
+    },
+  );
+});
diff --git a/src/components/features/files-tab/file-content-viewer.tsx b/src/components/features/files-tab/file-content-viewer.tsx
index 147218bb1..2a15f1135 100644
--- a/src/components/features/files-tab/file-content-viewer.tsx
+++ b/src/components/features/files-tab/file-content-viewer.tsx
@@ -18,11 +18,47 @@ interface FileContentViewerProps {
 const HTML_LIKE_EXTS = new Set(["html", "htm", "svg"]);
 const MARKDOWN_EXTS = new Set(["md", "markdown", "mdx"]);
 
+// Office/document formats we can't preview inline. The label doubles as the
+// allow-list (a present entry => Office doc) and feeds a clear, format-named
+// "no preview" message instead of the generic binary fallback.
+const OFFICE_DOCUMENT_LABELS: Record<string, string> = {
+  pptx: "PowerPoint",
+  ppt: "PowerPoint",
+  docx: "Word",
+  doc: "Word",
+  xlsx: "Excel",
+  xls: "Excel",
+};
+
 function getExtension(path: string): string {
   const idx = path.lastIndexOf(".");
   return idx === -1 ? "" : path.slice(idx + 1).toLowerCase();
 }
 
+/**
+ * Fallback shown when a file's bytes aren't previewable. Office documents
+ * (.pptx / .docx / .xlsx …) get a clear, format-named message; every other
+ * binary keeps the generic "binary file" string so the pane is never blank.
+ */
+function UnpreviewableFallback({ path }: { path: string }) {
+  const { t } = useTranslation("openhands");
+  const documentLabel = OFFICE_DOCUMENT_LABELS[getExtension(path)];
+  return (
+    <div
+      className="flex h-full w-full items-center justify-center text-sm text-[var(--oh-muted)]"
+      data-testid={
+        documentLabel
+          ? "file-content-viewer-unsupported-document"
+          : "file-content-viewer-binary-fallback"
+      }
+    >
+      {documentLabel
+        ? t(I18nKey.FILES$UNSUPPORTED_DOCUMENT, { type: documentLabel })
+        : t(I18nKey.FILES$BINARY_FALLBACK)}
+    </div>
+  );
+}
+
 /**
  * Renders the contents of a single workspace file. In `rich` mode we point
  * an iframe / <img> straight at the agent server's static workspace
@@ -82,14 +118,7 @@ export function FileContentViewer({ path, viewMode }: FileContentViewerProps) {
         />
       );
     }
-    return (
-      <div
-        className="flex h-full w-full items-center justify-center text-sm text-[var(--oh-muted)]"
-        data-testid="file-content-viewer-binary-fallback"
-      >
-        {t(I18nKey.FILES$BINARY_FALLBACK)}
-      </div>
-    );
+    return <UnpreviewableFallback path={path} />;
   }
 
   // ----- Rich mode: render HTML, markdown, images, PDFs from staticUrl. ----
@@ -129,14 +158,7 @@ export function FileContentViewer({ path, viewMode }: FileContentViewerProps) {
   }
 
   if (kind === "binary") {
-    return (
-      <div
-        className="flex h-full w-full items-center justify-center text-sm text-[var(--oh-muted)]"
-        data-testid="file-content-viewer-binary-fallback"
-      >
-        {t(I18nKey.FILES$BINARY_FALLBACK)}
-      </div>
-    );
+    return <UnpreviewableFallback path={path} />;
   }
 
   // Text-like content.
@@ -202,12 +224,5 @@ export function FileContentViewer({ path, viewMode }: FileContentViewerProps) {
 
   // Truly unknown / empty payload — show a fallback so the pane is never
   // blank.
-  return (
-    <div
-      className="flex h-full w-full items-center justify-center text-sm text-[var(--oh-muted)]"
-      data-testid="file-content-viewer-binary-fallback"
-    >
-      {t(I18nKey.FILES$BINARY_FALLBACK)}
-    </div>
-  );
+  return <UnpreviewableFallback path={path} />;
 }
diff --git a/src/i18n/translation.json b/src/i18n/translation.json
index 9d8de6c0e..05701c383 100644
--- a/src/i18n/translation.json
+++ b/src/i18n/translation.json
@@ -21640,6 +21640,23 @@
     "uk": "Двійковий файл – попередній перегляд недоступний",
     "ca": "Fitxer binari – previsualització no disponible"
   },
+  "FILES$UNSUPPORTED_DOCUMENT": {
+    "en": "Preview isn't available for {{type}} files.",
+    "ja": "{{type}} ファイルのプレビューは利用できません。",
+    "zh-CN": "{{type}} 文件无法预览。",
+    "zh-TW": "{{type}} 檔案無法預覽。",
+    "ko-KR": "{{type}} 파일은 미리 보기를 사용할 수 없습니다.",
+    "no": "Forhåndsvisning er ikke tilgjengelig for {{type}}-filer.",
+    "it": "L'anteprima non è disponibile per i file {{type}}.",
+    "pt": "A visualização não está disponível para arquivos {{type}}.",
+    "es": "La vista previa no está disponible para archivos {{type}}.",
+    "ar": "المعاينة غير متاحة لملفات {{type}}.",
+    "fr": "L'aperçu n'est pas disponible pour les fichiers {{type}}.",
+    "tr": "{{type}} dosyaları için önizleme kullanılamıyor.",
+    "de": "Für {{type}}-Dateien ist keine Vorschau verfügbar.",
+    "uk": "Попередній перегляд недоступний для файлів {{type}}.",
+    "ca": "La previsualització no està disponible per als fitxers {{type}}."
+  },
   "FILES$LOADING_FILES": {
     "en": "Loading files…",
     "ja": "ファイルを読み込んでいます…",