The short answer
PDF, JPG, PNG, WebP, SVG, and plain text convert reliably in your browser with no upload. DOCX, PPTX, XLSX, KEY, PAGES, NUMBERS, ODT, ODS, ODPcannot — their layout engines are not available in the browser. For those, use the source app's built-in “Save As PDF” or accept that an online converter will upload your file.
Why some formats fail in the browser
A file format is just a container. Whether you can convert it depends on whether your environment has the right renderer — the code that knows how to paint that container into pixels or pages. Browsers ship renderers for HTML, JPG, PNG, WebP, SVG, PDF (via PDF.js), and plain text. They do not ship a Microsoft Word renderer, a PowerPoint renderer, an Excel renderer, or an Apple Keynote renderer.
Those office-suite renderers each took 20–30 years of engineering to build. They handle thousands of edge cases: widow/orphan control, hyphenation, table-row flow, embedded fonts, conditional formatting in spreadsheets, slide master inheritance. Open-source attempts (LibreOffice, Apache OpenOffice) come close but are also massive C++ codebases that have never been faithfully ported to run in a browser tab.
So when an online tool claims to convert DOCX → PDF in your browser, one of three things is happening: (a) it's actually uploading despite what the marketing says, (b) it's using a partial JavaScript renderer like docx-preview that approximates the layout, or (c) it's producing a distorted output and hoping you do not notice. None of these are good.
What actually works browser-side
| Format | Why it works | On PDFGami |
|---|---|---|
| pdf-lib + PDF.js parse and write PDFs in JS | Merge / Split | |
| JPG / PNG / WebP | Canvas API decodes and encodes natively | Image Converter |
| SVG | Browsers render SVG natively; Canvas rasterizes | Image Converter |
| TXT, code files | Plain text needs no layout engine | Combine to PDF |
What does not work and what to do instead
For each of these, the source application already has a built-in “Save As PDF” or “Export To PDF” that produces a perfectly faithful PDF locally. Use that, then bring the PDF into PDFGami for merging, splitting, compressing, or signing.
Apple Keynote, Pages, Numbers (.key, .pages, .numbers)
Apple iWork formats use a proprietary container that wraps Protocol Buffers binary streams (Apple calls this the iWork Archive, or IWA). The format is undocumented; LibreOffice's libetonyek library can partially read it but is not designed for accurate page rendering. There is no production-grade browser-side library.
Open the file in Keynote / Pages / Numbers on a Mac, iPhone, or iPad, then choose File → Export To → PDF. No Mac? Go to iCloud.com, sign in, open the file in the web version of the app, and use its export. Both options run the actual Apple rendering engine, which is the only way to get a faithful PDF.
Microsoft Office (DOCX, PPTX, XLSX)
The OOXML format is documented (ECMA-376), but the rendering rules — how a table flows across page breaks, how headers and footers interact with section breaks, how spreadsheet cells overflow — live in Word, PowerPoint, and Excel. PDFGami used to attempt browser-side DOCX conversion via docx-preview; the output frequently collapsed multi-page documents onto a single page. We removed the feature in v1.2.0 to keep our quality promise.
In Word / PowerPoint / Excel: File → Save As → PDF, or on macOS File → Export → PDF. Free alternatives: LibreOffice (desktop) and Google Docs / Slides / Sheets all produce reliable PDFs from these formats.
OpenDocument (ODT, ODS, ODP)
Same issue as OOXML: the format is open, but faithful rendering still requires a desktop suite. Use LibreOffice or another OpenDocument-aware editor and export to PDF locally.
A practical rule of thumb
If the file format is “owned” by a particular desktop app (Word, PowerPoint, Excel, Keynote, Pages, Numbers, AutoCAD, Adobe Illustrator), the only way to get a faithful PDF is to use that app — or pay for a service that runs it. Browser-only conversion is a category mistake for those formats.
If the file format is an open web standard (PDF, JPG, PNG, WebP, SVG, plain text), browser-only conversion is the right tool. It is faster, more private, and free.
Frequently asked questions
Can I convert an Apple Keynote (.key) file to PDF online without uploading it?
Not reliably. The Keynote file format is a proprietary binary format Apple does not document publicly, and no browser-side library can faithfully render it. Cloud-based converters can do it because they run the actual Keynote app on a Mac in their datacenter — which means uploading your file. The safest free option is to open the file in Keynote on a Mac (or iCloud.com Keynote) and use File → Export To → PDF.
Can I convert a Word document (DOCX) to PDF entirely in the browser?
Not at a quality you can trust. DOCX layout depends on Word's rendering engine — fonts, page breaks, table flow, header/footer behavior — and no browser-side library replicates it faithfully. PDFGami used to attempt this and the output frequently collapsed multiple pages onto one. We removed the feature in v1.2.0 rather than ship a broken result. Use Word's built-in "Save As PDF" instead.
Why do server-based converters work for DOCX and KEY when browser ones do not?
Server converters run the actual originating application (Word, Keynote, LibreOffice) on a backend machine to render the document, then send back the PDF. That works, but it means your file is uploaded, processed by third-party software, and stored on disk for some retention window. For confidential documents (contracts, medical records, financial statements) that trade-off is usually unacceptable.
Which formats convert reliably in a browser today?
PDF (merge, split, compress, sign, extract pages), JPG, JPEG, PNG, WebP, SVG (rasterize), and plain text (TXT, code files). These work because the browser ships with native or WebAssembly support for them. Image-format conversions in particular are essentially free thanks to the Canvas API.
Is it safe to upload my Word/Keynote/Excel file to a cloud converter?
It depends on the document. For a public marketing brochure, sure. For an NDA, a tax return, a medical lab result, or anything else you would not want sitting on a third party's server for some retention window, no — assume the file persists until you have a clear deletion guarantee, and do not use a free cloud converter for it. Use the source app's built-in export instead.
What about HEIC (iPhone photo) files?
HEIC is technically convertible in the browser via the libheif WebAssembly decoder, but it adds a noticeable bundle download. We are evaluating it; for now, on macOS export to JPG via Photos, or on Windows install the free HEIF Image Extension from the Microsoft Store and then convert via our Image Converter.
Try the formats that actually work
PDF, JPG, PNG, WebP, SVG — converted locally in your browser, no upload. Pick a tool below.