offline_document_viewer 0.1.0

View PDF, Word, Excel and PowerPoint documents fully offline. Renders on the device with bundled open-source engines — no network, no server, no cloud.

offline_document_viewer

View PDF, Word, Excel and PowerPoint documents in Flutter — entirely on the device. No server, no conversion API, no network permission. The rendering engines ship inside the package.

DocumentView(source: DocumentSource.file('/path/to/report.xlsx'))

That is the whole minimum. The widget draws the document and nothing else — no app bar, no toolbar, no page counter — so it drops into your design instead of fighting it.

_{The example app. Everything except the document itself belongs to the app — the package contributes the rendering surface.}

Why this exists

Android has no system component that renders Office documents. The usual workaround is a WebView pointed at Google Docs Viewer or Office Online, which requires an internet connection and sends the document to a third party. Commercial SDKs do work offline, but they are enterprise-priced and closed.

This package takes the third road: open-source engines, bundled, running on the device.

Supported formats

Format	Fidelity	Engine
.pdf	Full	PDFium, native — never touches the WebView
.docx .docm	High	docx-preview (patched)
.xlsx .xlsm	High	SheetJS + this package's own style layer
.pptx .pptm	High	PPTXjs (patched)
.xls	Values, no styling	SheetJS
.csv .tsv	Full	SheetJS
.rtf	Text and formatting	Converted to HTML in Dart
.doc .ppt	Text only, labelled	OLE compound file reader, in Dart

Every one of these is verified rendering on a device, not just in unit tests.

.rtf, .doc and .ppt are handled entirely in Dart — no JavaScript engine is involved. RTF keeps paragraphs, emphasis, colours, alignment and lists. The two legacy binary formats have no open-source on-device layout engine, so they are shown as text and say so: a clear text view beats a half-working fidelity attempt, and DocumentFormat.fidelity reports textOnly so your UI can too.

What Excel gets right that the underlying engine does not

SheetJS Community Edition reads cell fills but not borders, fonts or alignment; those are a Pro feature. This package parses xl/styles.xml, xl/theme/theme1.xml and the per-sheet style indices itself, so you get border styles and weights, theme colours with tint and shade, the indexed palette, bold/italic/underline/strike, super- and subscript, horizontal and vertical alignment, wrapping, indent, rotated text, merged cells, column widths, row heights, hidden rows and columns, and frozen panes.

Installation

dependencies:
  offline_document_viewer: ^0.1.0

No asset declarations, no platform channels to register — the engines and fonts travel with the package.

Android

minSdkVersion 21 or higher.

If your project uses Android Gradle Plugin 9, add this to your app's pubspec.yaml:

dependencies:
  flutter_inappwebview: ^6.2.0-beta.3

The 6.1.x line references a ProGuard file that AGP 9 rejects, which fails the build before your code is compiled. This package's constraint is deliberately left open so you are not forced onto a pre-release when you do not need one.

iOS

iOS 12 or higher — the floor set by the bundled PDFium and WebView plugins. No Info.plist entries are required: the package requests no permissions and opens no network connections.

The bundled example/ app targets iOS 14, because the file picker it uses to demonstrate the package needs it. That is the example's requirement, not the package's.

Usage

With your own chrome

final controller = DocumentViewController();

@override
void dispose() {
  controller.dispose();
  super.dispose();
}

DocumentView(
  source: DocumentSource.bytes(bytes, name: 'q3-report.pptx'),
  controller: controller,
  placeholderBuilder: (context) => const MySkeleton(),
  errorBuilder: (context, failure) => MyError(failure: failure),
  onReady: (info) => debugPrint('${info.unitCount} slides in ${info.renderDuration}'),
);

// elsewhere
await controller.search('revenue');   // '' clears the highlight
await controller.goTo(3);
controller.info?.outline;             // headings, sheet names, slide titles

DocumentViewController is a ChangeNotifier. Listen to it for status, position, searchHits, info and failure.

Sources

DocumentSource.file(path)                     // from disk
DocumentSource.bytes(bytes, name: 'a.docx')   // already in memory
DocumentSource.asset('assets/manual.pdf')     // from your bundle

Bytes are read once and copied into a private workspace, so a stale iOS security-scoped bookmark or a revoked Android URI permission cannot break an already-opened document.

Failures are typed, not strings

errorBuilder: (context, failure) => Text(switch (failure) {
  EncryptedDocumentFailure() => 'This document is password protected',
  TooLargeFailure(:final sizeBytes) => 'Too large: $sizeBytes bytes',
  UnsupportedFormatFailure(:final extension) => '.$extension is not supported',
  _ => 'Could not open this document',
}),

DocumentFailure is sealed, so a switch over it is exhaustive. Each failure also carries a recovery hint — retry, reselect the file, ask for a password, open elsewhere — and no user-facing text, because wording and translation belong to your app.

Validate before you show any UI

final report = DocumentPreflight.inspect(bytes: bytes, fileName: name);
if (report is DocumentFailure) {
  // reject with your own message
}

API

Type	Purpose
DocumentView	The widget. placeholderBuilder, errorBuilder, onReady, onFailure, renderTimeout
DocumentViewController	search(), goTo(), plus status, position, searchHits, info, failure
DocumentSource	.file() · .bytes() · .asset()
DocumentPreflight	Standalone validation, with its limits exposed as constants
DocumentFormat	Detected format, its fidelity and family
DocumentFailure	Sealed failure hierarchy with RecoveryHint

Security

Documents are untrusted input, and the package treats them that way.

• Preflight runs before any engine sees the bytes: empty files, size caps, entry-count caps, path traversal, and zip bombs. The zip central directory is read by hand so declared sizes are checked without inflating anything.
• No network. The WebView that hosts the Office engines carries a strict Content Security Policy with connect-src 'none', and every navigation outside the document's private workspace is refused. Remote references embedded in a document cannot phone home.
• No loosened file access. allowFileAccessFromFileURLs and allowUniversalAccessFromFileURLs stay off. On iOS the document bytes are streamed over the JavaScript bridge rather than fetched, precisely so those flags can remain disabled.
• Renderer crashes are contained. On Android an unhandled WebView renderer-process death takes the whole application down; it is intercepted and reported as a recoverable RendererFailure.

How the bridge works

Android and iOS deliberately diverge:

• Android — WebViewAssetLoader serving the workspace from the virtual https://appassets.androidplatform.net origin. Google's own recommendation: a real origin keeps the same-origin policy intact.
• iOS — WKWebView.loadFileURL with read access scoped to the workspace. A custom scheme handler is not used: on iOS 26, WebKit terminates pages loaded through a custom scheme that contain scripts.

Fitting the screen

Word pages, slides and spreadsheets are authored at a fixed width that is far wider than a phone. Each is scaled down to the viewport on render, which keeps every relationship in the document intact and leaves pinch-zoom available. Without it a document reads as broken rather than merely zoomed out — columns look misaligned and content appears to be missing.

Very wide spreadsheets stop scaling at 40% and scroll from there, so text never becomes unreadably small.

Size

Roughly 6 MB compressed. Most of that is fonts, and they are not optional: Office documents size their text boxes using Calibri, Cambria and Arial metrics, which exist on neither Android nor iOS. Without metric-compatible substitutes text overflows its box and fixed-position layouts drift — the difference is immediately visible, not cosmetic.

Known limits

• Spreadsheets are cut off past 3000 rows rather than exhausting memory; DocumentInfo.truncated tells you when that happened.
• Charts, conditional formatting, data validation and pivot tables are not rendered.
• PowerPoint does not apply normAutofit, and long lines can still break mid-word.
• .xls gives you values without styling — the legacy format's style data is not readable by the bundled engine.
• Password-protected documents are detected and reported, not opened.

Example

example/ is a small document library: format badges, search, an outline sheet and error copy, all built on DocumentView. It is the reference for how the package expects to be used.

cd example && flutter run

Contributing

Issues and pull requests are welcome. Before opening a PR:

flutter analyze          # must be clean, including public_member_api_docs
flutter test             # unit tests plus fixture and asset guards
./tool/check_js.sh       # parses the bundled JavaScript; needs Node

The bundled engines carry patches; each is marked /* PATCH: */ in the source and explained in THIRD_PARTY_NOTICES.md and doc/. If you change one, record it there too — the licences require it.

Licence

MIT, plus the bundled engines and fonts under their own licences. See THIRD_PARTY_NOTICES.md — if you ship an app with this package, you need to carry those notices. The licence texts are bundled as assets so you can show them from an about screen:

await rootBundle.loadString(
  'packages/offline_document_viewer/assets/licenses/LICENSE-liberation',
);