Convert JPG to PDF entirely locally without uploading sensitive scans: Windows selects images and prints to Microsoft Print to PDF, one image per PDF or multiple combined in order, while Mac uses Finder's Create PDF quick action or Preview's Export as PDF. A Python script with Pillow or img2pdf handles bulk, with img2pdf embedding the JPG without recompressing. For document scans choose embed as is approaches that keep text crisp rather than converters that re render and soften legibility.

Convert JPG to PDF | TechQueries

I have folders of scanned document photos as JPGs and need them as PDFs, sometimes one PDF per image and sometimes many images combined into one PDF.

What is the simple reliable way for both, without uploading sensitive scans to random websites?

The without uploading sensitive scans instinct is right, document scans should not go to random web converters, so the answer stays entirely on your own machine. Both shapes, by platform:

Windows, built in: select the JPGs, right click, Print and choose Microsoft Print to PDF as the printer. One selected image makes one PDF, multiple selected images print into one PDF in the order shown, the combine case handled natively. The Photos app also prints to PDF the same way. No download, nothing uploaded, the OS doing it.

Mac, built in: select the images in Finder, right click, Quick Actions, Create PDF, which combines selected images into a single PDF instantly or open in Preview and File, Export as PDF for a single one. Preview also lets you drag images together and export the combined set, the Mac's native path for both shapes.

The scripted route for volume or automation: a short Python script with Pillow and its PDF save, or img2pdf which preserves the JPG data without recompressing, converts folders in bulk locally, worth it for recurring batches and giving control over page size and whether images combine or stay separate. img2pdf specifically avoids the quality loss some tools introduce by recompressing already compressed JPGs.

The quality note for scanned documents: converting a JPG to PDF should not recompress the image, since a scan recompressed loses legibility, so tools that embed the JPG as is, img2pdf explicitly and the OS print routes generally, keep the scan crisp, while some converters that re render can soften text. For document scans, the embed as is approach preserves what a scan needs, readable text.

Microsoft Print to PDF combined my multi page scans into single PDFs perfectly, all local, nothing uploaded which mattered for these documents. Used img2pdf for the big folder to avoid recompression and the text stayed sharp. The recompress warning was exactly relevant for scans.