What a JFIF file actually is
JFIF is not a strange new format. It's the same JPEG image you already know, just saved with a different extension. Windows, some browsers and certain websites save pictures as .jfif when you use “Save image as”, which is why so many people suddenly find a JFIF in their Downloads folder and can't attach it where they need it.
The trouble is that some upload forms check the extension, not the content. A portal that accepts JPG may reject a .jfif, and a few older programs won't open it at all. When what you need in the end is a PDF, you can skip renaming and convert the JFIF straight into a document.
When you need the picture as a PDF
Plenty of applications ask for documents in PDF only: job portals, school and university systems, insurance claims, rental applications, tax and benefits websites. If the proof you have is an image saved as JFIF, maybe a receipt you downloaded, a scanned certificate someone sent you or a screenshot of a confirmation, turning it into a PDF is the quickest way to get it accepted.
You can also gather several pictures into one file. Select every JFIF at once, together with any JPG or PNG images, put them in the right order and they become consecutive pages of a single PDF. The person on the other side opens one attachment instead of ten.
Page size, orientation and margins
Letter is the usual paper size in the US and Canada, while A4 is the standard in the UK, India and most other countries. Pick the one used by whoever will print or review the document. Choose “Same as image” when you want each page to match the picture exactly, with no white border around it.
Orientation can be automatic, portrait or landscape. Automatic turns each page to fit its picture, which helps when you mix tall and wide images. Margins can be none, small or large; a small margin looks tidy on paper and keeps the edges of the image away from the printer's unprintable area.
Private and free
The conversion happens inside your browser. Your JFIF images are never uploaded or stored anywhere, which matters when they show an ID card, a bank letter or a medical note. There's no account, no email, no watermark and no daily limit. The only practical cap is the memory of your device with very large batches.
Because JFIF is JPEG inside, the images are placed in the PDF without the kind of heavy recompression that blurs text, as long as they don't need rotating. If the final PDF is too heavy for an email or a portal, send it to Compress PDF next without selecting it again.