diff --git a/__tests__/opened.spec.ts b/__tests__/opened.spec.ts
new file mode 100644
index 0000000..bdbb364
--- /dev/null
+++ b/__tests__/opened.spec.ts
@@ -0,0 +1,87 @@
+/*!
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+import { File } from '@nextcloud/files'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+const post = vi.fn()
+const isPublicShare = vi.fn(() => false)
+const getCurrentUser = vi.fn<() => { uid: string } | null>(() => ({ uid: 'alice' }))
+const logger = { debug: vi.fn(), warn: vi.fn() }
+
+vi.mock('@nextcloud/axios', () => ({ default: { post } }))
+vi.mock('@nextcloud/router', () => ({ generateOcsUrl: (url: string) => `/ocs/v2.php/${url}` }))
+vi.mock('@nextcloud/sharing/public', () => ({ isPublicShare: () => isPublicShare() }))
+vi.mock('@nextcloud/auth', () => ({ getCurrentUser: () => getCurrentUser() }))
+vi.mock('../lib/services/logger.ts', () => ({ logger }))
+
+const { reportOpened } = await import('../lib/services/opened.ts')
+
+const file = new File({
+	source: 'https://cloud.example.com/remote.php/dav/files/alice/a.jpg',
+	root: '/files/alice',
+	owner: 'alice',
+	mime: 'image/jpeg',
+	id: 42,
+})
+
+describe('reportOpened', () => {
+	beforeEach(() => {
+		post.mockReset().mockResolvedValue({})
+		isPublicShare.mockReturnValue(false)
+		getCurrentUser.mockReturnValue({ uid: 'alice' })
+		logger.debug.mockReset()
+		logger.warn.mockReset()
+	})
+
+	it('reports the file by its id', async () => {
+		await reportOpened(file)
+
+		expect(post).toHaveBeenCalledWith('/ocs/v2.php/apps/files/api/v1/opened', { fileId: 42 })
+	})
+
+	it('reports nothing for a guest', async () => {
+		getCurrentUser.mockReturnValue(null)
+
+		await reportOpened(file)
+		expect(post).not.toHaveBeenCalled()
+	})
+
+	it('reports nothing on a public share page', async () => {
+		isPublicShare.mockReturnValue(true)
+
+		await reportOpened(file)
+		expect(post).not.toHaveBeenCalled()
+	})
+
+	// Talk hands a logged-in user files it took from a share
+	it('reports nothing for a file reached through a public share', async () => {
+		const shared = new File({
+			source: 'https://cloud.example.com/public.php/dav/files/abc/a.jpg',
+			root: '/files/abc',
+			owner: null,
+			mime: 'image/jpeg',
+			id: 42,
+		})
+
+		await reportOpened(shared)
+		expect(post).not.toHaveBeenCalled()
+	})
+
+	// A server before 36, or a file the user cannot see: nothing to warn about
+	it('only logs for debugging when the server answers 404', async () => {
+		post.mockRejectedValue(Object.assign(new Error('Not found'), { response: { status: 404 } }))
+
+		await expect(reportOpened(file)).resolves.toBeUndefined()
+		expect(logger.debug).toHaveBeenCalledOnce()
+		expect(logger.warn).not.toHaveBeenCalled()
+	})
+
+	it('warns, without failing, when the request fails otherwise', async () => {
+		post.mockRejectedValue(new Error('offline'))
+
+		await expect(reportOpened(file)).resolves.toBeUndefined()
+		expect(logger.warn).toHaveBeenCalledOnce()
+	})
+})
diff --git a/lib/services/opened.ts b/lib/services/opened.ts
new file mode 100644
index 0000000..72dcaa0
--- /dev/null
+++ b/lib/services/opened.ts
@@ -0,0 +1,39 @@
+/*!
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+import type { IFile } from '@nextcloud/files'
+
+import { getCurrentUser } from '@nextcloud/auth'
+import axios from '@nextcloud/axios'
+import { generateOcsUrl } from '@nextcloud/router'
+import { isPublicShare } from '@nextcloud/sharing/public'
+import { publicShareOf } from '../utils/publicShare.ts'
+import { logger } from './logger.ts'
+
+/**
+ * Tell the server the user opened a file, so apps like recommendations
+ * know what they work with. Reading a file says nothing about that: sync
+ * clients and previews read files all the time.
+ *
+ * Only a user's own files: a guest or a file reached through a public
+ * share has no file id the user could open. Opening is never held up by
+ * it, and a server before 36 has no such endpoint.
+ *
+ * @param file - The file the viewer was asked to open
+ */
+export async function reportOpened(file: IFile): Promise<void> {
+	if (getCurrentUser() === null || isPublicShare() || publicShareOf(file) || file.fileid === undefined) {
+		return
+	}
+
+	try {
+		await axios.post(generateOcsUrl('apps/files/api/v1/opened'), { fileId: file.fileid })
+	} catch (error) {
+		if ((error as { response?: { status?: number } }).response?.status === 404) {
+			logger.debug('The server does not know this file or how to report opening it', { file, error })
+			return
+		}
+		logger.warn('Could not report the file as opened', { file, error })
+	}
+}
diff --git a/lib/views/Viewer.vue b/lib/views/Viewer.vue
index 256f5c3..aab0bb3 100644
--- a/lib/views/Viewer.vue
+++ b/lib/views/Viewer.vue
@@ -366,6 +366,7 @@ import { getHandlers, isHandlerEnabled } from '../handlers.ts'
 import { getHandlerForFile } from '../helpers/handlerHelper.ts'
 import { fetchFolderContent } from '../services/dav.ts'
 import { logger } from '../services/logger.ts'
+import { reportOpened } from '../services/opened.ts'
 import { dispatchViewerEvent, ViewerSession } from '../session.ts'
 import { prepareDownload } from '../utils/beforeDownload.ts'
 import { canDownload } from '../utils/canDownload.ts'
@@ -1356,6 +1357,8 @@ async function showFiles(files: IFile[], file?: IFile, options?: ViewerOptions,
 	if (!isSameFile) {
 		loading.value = true
 		pendingLoads.value = 1
+		// Only what was asked for: stepping through the others is browsing
+		reportOpened(file)
 	}
 	// A failure to open something else earlier is not this file's problem
 	errorString.value = null