Can I convert files without uploading them?

Yes. OnlyFiles offers many browser-based conversions that run entirely on your device — including all image conversions, HEIC to JPG, PDF to/from images, CSV/Excel conversions, and PDF merge/split. Document conversions (like Word to PDF) and audio conversions require a secure server, but files are deleted immediately after processing.

Is browser-based file conversion safe?

Browser-based conversion is the safest option because your files never leave your device. No server stores, accesses, or logs your data. OnlyFiles uses open-source JavaScript libraries that run entirely in your browser tab.

Which file conversions can run in the browser?

On OnlyFiles, browser-based conversions include: all image format conversions (JPG, PNG, WebP, GIF, BMP, SVG), HEIC to JPG/PNG, PDF to JPG/PNG, JPG/PNG to PDF, CSV to Excel, Excel to CSV, PDF merge, and PDF split. Document conversions (DOCX, PPTX) and audio conversions (MP3, WAV) require server processing.

Does browser-based conversion work offline?

Yes. Once an OnlyFiles browser-based conversion page loads, you can disconnect from the internet and continue converting. The JavaScript libraries are already loaded in your browser. This only applies to browser-based tools — server-side conversions require an internet connection.

How to convert files without uploading them

Most online file converters upload your files to their servers. OnlyFiles takes a different approach: many of its conversion tools run entirely in your browser using JavaScript. Your files never leave your device for these conversions — no server ever sees them.

Why browser-based conversion matters

Uploading sensitive documents to a server introduces risk. Your file could be intercepted, logged, or stored longer than you expect. Browser-based conversion eliminates that risk entirely. The code runs on your computer in your browser tab, so your data never touches a server. The processing is also instant — no upload wait, no server queue, no download wait. And because your browser does all the work, these conversions even work offline after the page loads.

Which OnlyFiles tools run in the browser

The following conversions run 100% in your browser with zero uploads:

Image conversions: JPG ↔ PNG, JPG ↔ WebP, PNG ↔ WebP, SVG → PNG/JPG, GIF → PNG/JPG, BMP → PNG/JPG
iPhone photos: HEIC → JPG, HEIC → PNG
PDF ↔ Image: PDF → JPG, PDF → PNG, JPG → PDF, PNG → PDF
Spreadsheets: CSV → Excel, Excel → CSV
PDF tools: Merge PDFs, Split PDF

Which conversions need a server

Some conversions require specialized software that can't run in a browser. OnlyFiles uses a secure server for these, and files are deleted immediately after processing:

Document conversions: Word → PDF, PDF → Word, PowerPoint → PDF (uses LibreOffice)
Audio conversions: MP3 → WAV, WAV → MP3 (uses FFmpeg)
Compression: PDF, image, DOCX, and PPTX compression (uses Ghostscript/Sharp)

For these server-side tools, your file is uploaded over HTTPS, converted, and the original is deleted immediately. Nothing is stored, logged, or retained.

How the browser-based tools work

OnlyFiles uses well-established open-source JavaScript libraries that run entirely in your browser. Image conversions use the HTML5 Canvas API, a standard browser feature. PDF operations use pdf.js for reading, jsPDF for creating, and pdf-lib for merging and splitting. Spreadsheet conversions use SheetJS. All of these are open-source, widely used, and run 100% in JavaScript inside your browser tab.

How to verify no upload happens

You can verify this yourself on any browser-based tool. Test 1: Disconnect from the internet. Load a browser-based conversion page while online. Disconnect your WiFi. Try converting a file — it works, proving no server call is made. Test 2: Check the network tab. Open your browser's developer tools (F12), go to the Network tab, and convert a file. You'll see zero network requests during conversion. This confirms processing happened locally.

Browser-based tools to try

Convert HEIC to JPG — Transform iPhone photos in your browser.

Convert JPG to PNG — Browser-based image conversion, no upload.

Convert PDF to JPG — Extract pages as images, no server upload.

Convert JPG to PDF — Turn images into PDF in your browser.

Convert CSV to Excel — Browser-based spreadsheet conversion.

Merge PDFs — Combine multiple PDFs without uploading.

Split PDF — Extract pages entirely in your browser.

All tools — See every conversion and compression tool.

Related tools & guides

HEIC format JPG format PNG format HEIC to JPG PNG to JPG JPG to PDF Compress images Compress PDF