Converting JPG to PDF places your picture on a page so photos and scans can be sent as a document rather than loose image files. The pixels are not altered for the better: a blurred photo of a receipt is just as blurred in the PDF, and any text in it remains part of the picture.
Transfers use HTTPS, and files converted on the free tier are deleted within 24 hours, so the result is not a long-term archive. Quality depends on the source file, so open the PDF file once before you share it.
FromJPGLossy
JPEG (Joint Photographic Experts Group)
The most widely used photo format, produced by nearly every camera, phone and scanner. JPEG compression shrinks files by discarding detail the eye tends to miss, and a JPG is a single image with no pages.
ToPDFLossless
PDF (Portable Document Format)
A document format (ISO 32000) made of pages that can hold text, vector graphics and images together. A PDF reader shows the same page on any device, which is why offices, courts and upload portals commonly ask for it.