Why a PDF rather than a folder of images
A single document travels better than a set of files. It keeps its page order, it cannot arrive with half the pages missing, it opens the same way on every device, and most systems that accept document uploads accept PDF and nothing else.
That is why photographing a paper document and converting to PDF is such a common task: the recipient wants one file that behaves like the paper did, not eight camera images named IMG_4471 through IMG_4478.
How images are embedded
The PDF format supports JPEG and PNG image data natively. When you add a file in either of those formats, its original compressed bytes are copied into the document untouched — no decoding, no re-encoding, and no quality loss at all. The image inside the PDF is bit-for-bit the image you started with.
WebP, AVIF, BMP and GIF have no such support. Those are decoded and re-encoded as JPEG at high quality on the way in. For a lossy source such as WebP that means one extra generation of compression; for a lossless source such as BMP it means the first. The tool reports which files went through that path rather than leaving you to guess.
Page size, orientation and margins
Choosing A4, Letter or Legal gives you a document with consistent, printable pages. Each image is scaled to fit inside the margins while keeping its aspect ratio, and centred — never cropped, and never enlarged beyond the space available.
Match each image does the opposite: every page becomes exactly the size of its image. Nothing is scaled and no white space is added, so the PDF is a faithful container rather than a layout. This is the right choice for screenshots, scanned artwork, and anything where added margins would be a distraction — and the wrong choice for anything destined for a printer.
The margin setting applies only to the fixed page sizes. Zero puts the image right up against the page edge, which looks striking on screen but risks being clipped by printers that cannot print edge to edge. Around half an inch is the safe default.
Common uses
- Turning phone photos of a paper document into one file to email
- Bundling receipts or invoices for an expense claim
- Assembling scanned artwork or a portfolio into a single document
- Packaging screenshots into a report or bug write-up
- Preparing ID or certificate photos for an application that requires PDF