JPG → PDF: when this matters
Government forms, expense reports, and applications almost always ask for a single PDF — not a folder of photos. Pulling multiple receipts, scans, or screenshots into one PDF makes them easy to email and sensible to file. Pick Auto-fit page size to make each PDF page match its image, or pick A4 / Letter for a uniform document that prints cleanly.
PDF → JPG: when this matters
Sometimes you need an image of a PDF page — to paste into a slide deck, embed in a Notion page, share on social media, or open with a basic image viewer. The exporter renders each page at 2× device resolution (great for retina screens) and saves as JPEG at ~92% quality, a sweet spot for text-heavy pages.
Privacy
Both directions run in your browser. JPG → PDF uses pdf-lib to embed images directly into a new PDF. PDF → JPG uses pdfjs (Mozilla's PDF renderer) to draw each page to a canvas, then exports the canvas as a JPEG. Nothing is uploaded.