Convert JPG images to PDF without Installing Software

The Browser-Based Privacy Advantage

If you take photos of sensitive documents—such as medical records, financial invoices, or personal identity cards—the last thing you should do is upload those JPGs to a random cloud server. Traditional online converters require you to upload your files, wait for their server to process them, and then download the result. This exposes your private data to potential breaches and relies entirely on their data retention policies.

OncePDF fundamentally changes this. We utilize modern WebAssembly technology to deliver the PDF generation engine directly to your browser. When you drop your images into our tool, your device's own processor does the compiling. Your files never touch our servers. This guarantees 100% privacy and allows for lightning-fast conversions regardless of your internet upload speed.

Understanding Aspect Ratios and Scaling

One of the biggest frustrations when turning photos into PDFs is dealing with stretched or distorted images. This happens when the aspect ratio (the proportional relationship between an image's width and height) of your photo doesn't perfectly match the aspect ratio of your chosen page size (like A4 or Letter).

• Using "Fit": This is our recommended setting. It scales your image up or down until it reaches the edge of the page, without altering its proportions. If the aspect ratios don't match, you will see white space on the sides (letterboxing). This guarantees your photo is never stretched or cropped.
• Using "Fill": This will stretch the image to cover every pixel of the page. It's only recommended if your source images already match the exact dimensions of your target page.
• Using "Auto" Page Size: This completely bypasses the aspect ratio problem by forcing the PDF page to shrink or grow to perfectly match the dimensions of your uploaded image.

Best Practices for Scanning Documents with a Phone

If you are using your smartphone camera as a makeshift scanner before converting the JPGs to a PDF, follow these golden rules to ensure professional results:

• Lighting is Everything: Rely on natural daylight if possible. Avoid using your phone's flash, which creates harsh glares on glossy paper and washes out ink.
• Keep it Flat and Parallel: Hold your phone directly above the document, perfectly parallel to the table. Taking a photo at an angle will cause keystone distortion, making the text look pinched.
• Use a Dark Background: Place your white document on a dark table or mat. This high contrast helps your camera autofocus clearly on the text and makes it easier for you to crop the edges later.
• Check the Focus: Always tap your screen to force the camera to focus on the smallest text on the page before snapping the photo.

Managing Final File Sizes

Modern smartphones take incredibly high-resolution photos. While a 12-megapixel photo looks beautiful, combining twenty of them into a PDF can easily result in a file exceeding 50MB. This will be instantly rejected by most email servers.

To combat this, OncePDF includes a built-in Image Quality slider right on the dashboard. By slightly reducing the quality percentage, our engine applies smart JPEG compression during the generation process, drastically shrinking the final PDF size while keeping the visual fidelity high enough for reading and printing. If you need even more aggressive reduction after the fact, you can run the finished document through our PDF Compressor.