Office Document Preview

Read-only preview of text documents, spreadsheets, slides and drawings inside a VS Code tab, rendered by a headless LibreOffice. No window opens unless you ask for one.

Status: stable. Everything it set out to do is in and verified -- three render routes, viewer tools, a conversion cache and a size-aware timeout -- with no known defects and 122 automated checks running against real documents.

Verified on Windows 11 with LibreOffice 26.2, and from a packaged .vsix on Ubuntu 22.04 with 7.3 and Fedora 44 with 26.2 -- versions years apart, converting identically. Not yet exercised: macOS, and the snap and flatpak builds, whose sandbox is detected and explained but never tested. What the extension deliberately does not do is in Known limitations.

What it does

Open a .docx, .xlsx or .pptx -- or a .odt, .vsdx, .rtf, .wpd or anything else LibreOffice can read -- and see it inside the editor, without leaving VS Code and without launching LibreOffice's interface.

Spreadsheets get one tab per sheet, which is why they do not go through PDF: paginating a sheet is the opposite of navigating it, and a copied selection would paste as flat text instead of a grid.

Slides keep their backgrounds, images and layout, because they are rendered from PDF rather than from an HTML dump.

Every view zooms the same way -- the - / + / Fit buttons, Ctrl with the mouse wheel, or Ctrl + / - / 0. The Select / Pan button switches between selecting text and dragging the page around; the middle mouse button drags in either mode. Text is selectable everywhere, including over the rendered PDF pages.

File extensions are named above because they are what you search for; the products that write them are not affiliated with this extension.

An unrecognised extension is attempted anyway rather than refused: LibreOffice reads well over a hundred formats, and a wrong guess only costs a failed conversion with a clear message.

A Paper / Editor theme button switches between the document's own colours on white paper and the editor's theme. Paper is the default, because exported office documents assume white paper.

Paper	Editor

Open externally hands the document to your system's default application, for when you need to do something a preview cannot do. For a format your system has nothing registered for -- common with ODF and the older formats -- the command Office Document Preview: Open in LibreOffice forces the one application that is guaranteed to be installed.

Requirements

LibreOffice must be installed. That is the only requirement -- there is no build step and no npm dependency.

The extension looks for soffice in the usual install locations before falling back to the PATH, because the standard Windows installer does not put it on the PATH. If it cannot find yours, set officeDocumentPreview.sofficePath to the full path of the executable.

Any reasonably recent LibreOffice works. Verified on Windows 11 with 26.2 and on Ubuntu 22.04 with the distribution's 7.3 -- versions years apart, converting the same documents identically. What has not been exercised: macOS, and the snap and flatpak builds, whose sandbox cannot read files outside your home directory. The extension detects that case and says so rather than failing mysteriously, but nobody has run it.

Settings

The conversion budget is not one number, because conversion time is not one number. Measured on this extension's own test documents:

So the budget is a base plus an allowance per megabyte, capped. Size is only a proxy -- the 10.6 MB deck takes longer than the 13.4 MB one because it has more slides -- so the allowance is generous. The ceiling is what still catches a conversion that is stuck rather than slow: a password-protected document waits for a prompt that never appears. Every one of those numbers is a setting.

While a conversion runs, the tab says so and counts, rather than sitting blank:

Converted documents are cached, so reopening a tab is instant. The key is the file's SHA-256, which is what makes the invalidation exact rather than approximate: edit the document and its entry is replaced immediately, while touching, copying or moving a file that has not changed keeps the work. Hashing costs milliseconds against the seconds above. The cache is cleaned two ways -- entries unused for cacheMaxAgeDays are swept when the extension starts, and the least recently used are dropped when cacheMaxBytes is exceeded.

Running it from source

There is nothing to build. Open the folder in VS Code and press F5; the extension runs in a development window. Then right-click a document in the explorer and choose Office Document Preview: Open Preview.

The preview is always asked for, never imposed: the editor registers with priority: "option", so double-clicking a .docx still opens it the way it always did.

To check everything that does not need the interface:

$env:ELECTRON_RUN_AS_NODE=1
& "<path to Code.exe>" scripts\smoke.js | Tee-Object -FilePath "$env:TEMP\smoke.txt" | Out-Null
Get-Content "$env:TEMP\smoke.txt"

That runs on the Node that VS Code ships inside Electron, so it works without Node installed.

It needs documents to convert, and it looks for them in private/samples/ -- a directory that is git-ignored and therefore empty in a fresh clone. Drop any office files in there and the bench will pick them up. Real documents are worth far more than synthetic ones here: every interesting bug this extension has had was found by a real file and missed by a made-up one.

Known limitations

• Spreadsheets are not paginated. They are shown as tables, one tab per sheet, deliberately: going through PDF would paginate a sheet, which is the opposite of navigating it. Print layout, page breaks and repeated headers are not shown.
• Nothing is editable. No cell editing, no formula recalculation, no slide animations, no comments or tracked changes. What you see is the result the file already carried. When you need any of that, Open externally hands the document to the application that can do it.
• No VS Code for the Web. vscode.dev and github.dev cannot launch a local process. Remote SSH and dev containers work, provided LibreOffice is installed on the remote host.
• Snap and flatpak builds of LibreOffice cannot read files outside your home directory, and fail with a permission error the extension can only report, not fix.

How it works

Each preview converts the file with soffice --headless --convert-to into a private temporary directory, then renders the result in a webview. Conversions are strictly serialised and hold a lock on the LibreOffice profile, because two at once against the same profile make one of them fail without any error at all.

The intermediate format is chosen per family: PDF for everything except spreadsheets, drawn page by page with a vendored PDF.js, and HTML for spreadsheets, one tab per sheet. Spreadsheets are the exception for a reason: going through PDF would paginate a sheet, and a copied selection would paste as flat text instead of a grid.

PDF.js (Apache-2.0) is vendored under media/pdfjs/. Only the two files needed to render are shipped; media/pdfjs/VENDORED.md records where they came from and what was left out.

License

MIT.